Organometallic Compounds

Organometallic Compounds HENRY GILMAN

Downloaded by 46.189.216.28 on May 1, 2014 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch001

Iowa State College, Ames, Iowa

The material presented is a n account of studies, largely completed, in several areas. A m o n g them is the report that methylmagnesium iodide is stable for very long periods in diethyl ether. In sharp contrast is the relative instability of some organolithium compounds in tetrahydrofuran. However, techniques have been developed for the preparation a n d use of RLi compounds in tetrahydrofuran. A m o n g the i n teresting reactions effected in tetrahydrofuran as a solvent or medium is the cleavage of some heterocycles by lithium; special, synthetically valuable coupling reactions; unusual ratios of carbonation products of 2-quinolyllithium a n d 1-isoquinolyllithium; a n d an improved metalation procedure for dibenzofuran which should be a p p l i c a b l e to other metalations carried out in tetrahydrofuran systems. ortho-Halophenyllithium compounds have been prepared in tetrahydrofuran, a n d the intermediate benzyne has been established b y the Wittig technique using furan.

A g e n e r a l a c c o u n t , p a r t l y o f a r e v i e w n a t u r e , i s p r e s e n t e d o f t h e r e l a t i v e reactivities of o r g a n o m e t a l l i c c o m p o u n d s , i n t e r c o n v e r s i o n s o f o r g a n o m e t a l l i c c o m p o u n d s , and the o r d e r o f a c t i v i t y o f some f u n c t i o n a l g r o u p s t o w a r d s selected o r g a n o m e t a l l i c compounds. I n a d d i t i o n , t h e r e is g i v e n a c o n d e n s a t i o n o f e x p e r i m e n t a l d a t a o n n e w e r s t u d i e s c a r r i e d o u t b y c o w o r k e r s s e v e r a l m o n t h s before t h i s p a p e r w a s p r e s e n t e d a t t h e s y m p o s i u m i n A p r i l 1957. Stability of an E t h e r Solution of Methylmagnesium Iodide. I n connection with studies o n t h e g e n e r a l r e a c t i o n s o f o r g a n o m e t a l l i c c o m p o u n d s , t h e s t a b i l i t y of Grignard reagents h a s l o n g b e e n o f i n t e r e s t . P r e v i o u s work (14) indicated that the normalities of d i e t h y l e t h e r s o l u t i o n s o f v a r i o u s G r i g n a r d reagents, as d e t e r m i n e d b y acid titration (23), r e m a i n e d e s s e n t i a l l y u n c h a n g e d f o r 4 m o n t h s . I t w a s n e c e s s a r y to protect the G r i g n a r d reagent s o l u t i o n s a d e q u a t e l y f r o m t h e a i r , b u t p a r a l l e l experiments with e t h y l m a g n e s i u m b r o m i d e i n t h e l i g h t a n d i n t h e d a r k i n d i c a t e d t h a t daylight had little effect o n t h e s t a b i l i t y o f t h e s o l u t i o n s . S o l u t i o n s o f m e t h y l m a g n e s i u m iodide are w i d e l y u s e d i n a n a l y t i c a l m e t h o d s b a s e d o n t h e T s c h u g a e f f - Z e r e w i t i n o f f (88,4$) analysis f o r a c t i v e h y d r o g e n , a n d a s a r e s u l t t h e i r s t a b i l i t y h a s b e e n s u b j e c t e d to some s t u d y . A s o l u t i o n o f m e t h y l m a g n e s i u m i o d i d e i n d i - n - a m y l e t h e r i s reported to be " s t a b l e f o r a m o n t h o r m o r e " (86). W h e n a d i i s o a m y l e t h e r s o l u t i o n of methylmagnesium iodide, prepared for use in an a p p a r a t u s d e s i g n e d for a n a l y s i s with Grignard reagents, was analyzed " i m m e d i a t e l y after its preparation a n d after it had remained 1

In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.


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in its receptacle, exposed to the light for months/' the composition of the solution was found to be invariable (29). In connection with the stability of solutions of organometallic compounds in general, it is of interest to compare the above reported stability of methylmagnesium iodide in various solvents with the stability of methyllithium. Methyllithium in diethyl ether and in di-n-butyl ether (5,16) has been shown to enjoy certain advantages over methylmagnesium halides in the Tschugaeff-Zerewitinoff analysis, partly because of its stability and partly because of the greater solubility of some -OLi compounds over -OMgX compounds. In studies on a modification of the Tschugaeff-Zerewitinoff determination, a di-n-butyl ether solution of methyllithium was stored in a Grignard machine (28) and the normality of the solution, as determined by gas analysis, was found to have decreased only from 0.777 to 0.764 during 4 months. This indicates that a di-n-butyl ether solution of methyllithium is sufficiently stable for use as a valuable supplement to solutions of methylmagnesium iodide in carrying out TschugaeffZerewitinoff analyses. Further evidence of the stability of methylmagnesium iodide was obtained recently when a sealed Carius tube containing 50 ml. of a diethyl ether solution of about 2N methylmagnesium iodide was opened after remaining sealed for 20 years. The normality of the solution was determined by both acid titration and gas analysis and found to be essentially the same as when the solution was first placed in the tube. Of particular significance is the fact that the normality values found by the two different methods of analysis are in close agreement. The normality values obtained by acid titration normally run slightly higher than those obtained by gas analysis, probably because of the presence of basic magnesium compounds formed by means other than hydrolysis of the Grignard reagent, such as ether cleavage and the reaction of the Grignard reagent with traces of water and/or oxygen. Any cleavage of the diethyl ether by the methylmagnesium iodide which might have occurred during the 20 years of storage would have been evidenced by an abnormal difference between the normality values found by acid titration and those found by gas analysis. The average difference was found to be 2.6%, well below the reported average difference of 3.9%. Positive identification of the material as a solution of methylmagnesium iodide .was made by preparing acet-a-naphthalide (7) and methylmercuric iodide (30) and checking their properties against those of their respective authentic specimens. A color test I (19), taken immediately after opening the sealed tube, was strongly positive. It would not be unreasonable to expect variations with other Grignard reagents and variations with other solvents—for example, it is known that methylmetallic compounds may differ appreciably from others (5,10,16,17). Some Reactions of o-Halophenyllithium Compounds. As a continuation of earlier studies concerned with o-halophenyllithium compounds (9), some of their reactions and possible routes by which these organometallic compounds couple to form new organolithium compounds have been investigated further. To obtain a better understanding of the various transformations, the elegant procedure of Wittig and Pohmer (41) was employed. These workers successfully interacted o-bromofluorobenzene with lithium amalgam in furan to obtain l,4-dihyclronaphthalene-l,4-endoxide (III), a strained molecule which has been formulated as arising via a Diels-Alder reaction between furan and the benzyne intermediate (II). Furthermore, the reactive species (II) has been postulated as being formed from o-fluorophenyllithium after the latter has been generated by the interaction of o-bromofluorobenzene and lithium amalgam. The same reaction in the absence of furan gives diphenylene and triphenylene (40). In view of these results it was hoped that furan could be used in a similar fashion to trap any intermediate which might arise during the break-down of o-halophenyllithium compounds (I). o-Fluoro- and o-chlorophenyllithium were prepared at —60° and —90°, respectively. A relatively large excess of furan was added in each case and then the mixtures were allowed to warm to —50° for the chloro isomer and In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

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— 10° for the fluoro i s o m e r . A s color test I was p o s i t i v e i n b o t h cases a t these t e m p e r a t u r e s , the m i x t u r e s were c a r b o n a t e d . T h e r u n involving o-bromochlorobenzene afforded 4 1 % of I I I a n d 1 1 % of 2 - c a r b o x y - 2 ' - c h l o r o b i p h e n y l ; w i t h o - b r o m o f l u o r o b e n zene the y i e l d of I I I was 6 7 % , w h i l e 4 % of 2 - c a r b o x y - 2 - f l u o r o b i p h e n y l was i s o l a t e d . /


A m o d i f i e d p r o c e d u r e was used w i t h o - d i b r o m o b e n z e n e , because i t was f o u n d i n p r e v i o u s studies t h a t o - b r o m o p h e n y l l i t h i u m is a s h o r t - l i v e d i n t e r m e d i a t e . Conse q u e n t l y , o - d i b r o m o b e n z e n e was a d d e d t o a m i x t u r e o f f u r a n a n d b u t y l l i t h i u m . T h e y i e l d of I I I was 6 8 % ; h o w e v e r , as m i g h t b e e x p e c t e d , n o a c i d was i s o l a t e d .

α

I (X = C1 or F)

- Ο II

F r o m t h e f o r e g o i n g results i t i s c l e a r t h a t i n the case of o - c h l o r o - a n d o - f l u o r o p h e n y l l i t h i u m some r e a c t i v e i n t e r m e d i a t e is c o m p e t i t i v e l y r e a c t i n g w i t h f u r a n a n d w i t h I . F u r t h e r m o r e , evidence substantiates that such a competitive reaction occurs o n l y w h e n the o r g a n o l i t h i u m c o m p o u n d i s f o r m e d first i n d e p e n d e n t l y of t h e o t h e r r e a c t a n t s . I n o r d e r t o a s c e r t a i n t h a t no m e t a l a t i o n r e a c t i o n ensued b e t w e e n f u r a n a n d I f o l l o w e d b y a n o t h e r s i m i l a r m e t a l a t i o n b e t w e e n the halobenzene a n d 2 - f u r y l l i t h i u m at a w a r m e r t e m p e r a t u r e , a n a t t e m p t was m a d e t o m e t a l a t e c h l o r o b e n z e n e u n d e r c o n d i t i o n s used f o r the c o m p e t i t i v e r e a c t i o n s . N o I V was d e t e c t e d a f t e r c a r b o n a t i o n ; m o s t of the chlorobenzene was r e c o v e r e d . A t t h i s t i m e t h e m o s t p l a u s i b l e e x p l a n a t i o n f o r t h e presence of c o u p l i n g p r o d u c t i n t h e c o m p e t i t i v e r e a c t i o n i s one i n v o l v i n g I I , a l t h o u g h a n a l t e r n a t i v e e x p l a n a t i o n has b e e n p r o p o s e d r e c e n t l y f o r a r e l a t e d r e a c t i o n (31). I n t u i t i v e l y the h a l i d e i n I w o u l d n o t b e e x p e c t e d t o b e d i s p l a c e d b y a n u c l e o p h i l e because t h e h i g h e l e c t r o n density i n the position adjacent to the chlorine a t o m should hinder such a n a p p r o a c h . A l s o , n u c l e o p h i l i c a r o m a t i c s u b s t i t u t i o n reactions are f a c i l i t a t e d b y e l e c t r o n - w i t h d r a w i n g g r o u p s a n d n o t e l e c t r o n - d o n a t i n g s u b s t i t u e n t s (3). I t i s c o n c e i v a b l e t h a t t h e a n i o n of I m a y d i s p l a c e t h e h a l o g e n i n a n o t h e r m o l e c u l e of I e i t h e r j u s t before o r d u r i n g the f o r m a t i o n of the r e a c t i v e i n t e r m e d i a t e I I . I t has b e e n s h o w n t h a t b e n z y n e c a n be f o r m e d v i a e i t h e r a stepwise o r c o n c e r t e d m e c h a n i s m , d e p e n d i n g o n t h e h a l o g e n b e i n g e l i m i n a t e d w h e n m e t a l a t i o n r e a c t i o n s are i n v o l v e d . H o w e v e r , i n t h i s case these findings d o n o t necessarily a p p l y , because i t c a n n o t b e a s s u m e d t h a t t h e i n i t i a l step is s i m i l a r i n b o t h cases (34). T h e r a p i d conversion of o - b r o m o p h e n y l l i t h i u m t o I I d i d not allow its p r e p a r a t i o n p r i o r t o t h e a d d i t i o n o f f u r a n , a n d , as a r e s u l t , t h e c o n c e n t r a t i o n o f o - b r o m o p h e n y l l i t h i u m p r o b a b l y was so s l i g h t t h a t t h e m a i n r e a c t i o n was b e t w e e n I I a n d f u r a n . T h e reaction p a t h leading to I I I might involve a nucleophilic attack of I o n furan o r the m o r e p r o b a b l e r e a c t i o n of I I w i t h f u r a n . O f t h e tw o p o s s i b i l i t i e s , i t a p p e a r s b e t t e r t o r a t i o n a l i z e o n t h e basis t h a t I I is t h e k e y i n t e r m e d i a t e . I f I i s c o n s i d e r e d as b e i n g t h e a t t a c k i n g species, the f o l l o w i n g p a t h m i g h t be e x p e c t e d . r



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E v i d e n c e i n d i c a t e s t h a t a n i n t e r m e d i a t e s u c h as V is less l i k e l y t o u n d e r g o r i n g closure t o g i v e t h e h i g h l y s t r a i n e d m o l e c u l e I I I t h a n w o u l d a n i n t e r m e d i a t e a r i s i n g f r o m i n t e r a c t i o n o f I I w i t h f u r a n . I f V were f o r m e d as a n i n t e r m e d i a t e , r i n g closure a t s u c h a l o w t e m p e r a t u r e w o u l d b e d o u b t f u l i n v i e w o f p o l a r effects a n d f o r m a t i o n o f t h e s t r a i n e d m o l e c u l e I I I . P r e v i o u s studies s h o w e d t h a t a n i n t e r m e d i a t e s u c h as 2 - ( o - c h l o r o p h e n y l ) - 2 ' - l i t h i o b i p h e n y l does n o t u n d e r g o r i n g closure b e l o w a p p r o x i m a t e l y —50° t o g i v e t h e p l a n a r , n o n s t r a i n e d s y s t e m , t r i p h e n y l e n e . T h e f o r m a t i o n o f V v i a I i s u n p r e c e d e n t e d , as t h e r e i s n o k n o w n i n s t a n c e w h e r e i n f u r a n i s a t t a c k e d i n s u c h a m a n n e r . I n f a c t , u n d e r these c o n d i t i o n s f u r a n i s i n e r t t o such a n attack a n d a t w a r m e r temperatures the only product formed is 2 - f u r y l l i t h i u m . I n general, m e t a l a t i o n reactions proceed smoothly only a t r o o m temperature o r higher w h e n d i e t h y l e t h e r i s t h e s o l v e n t (18). I n d i s t i n g u i s h i n g b e t w e e n t h e t w o p a t h s i t is n o t p e r t i n e n t w h e t h e r t h e i n t e r a c t i o n of b e n z y n e w i t h f u r a n is a p o l a r r e a c t i o n o r a f o u r - c e n t e r t y p e o f r e a c t i o n . A s t h e r e is n o s h a r p l i n e b e t w e e n t h e l a t t e r t w o t y p e s o f r e a c t i o n m e c h a n i s m s , i t i s difficult t o r a t i o n a l i z e b y w h i c h one t h e b e n z y n e i n t e r a c t s w i t h f u r a n (26). O n t h e basis o f the a f o r e - m e n t i o n e d d i s c u s s i o n w h e r e i n I I has b e e n v i s u a l i z e d as the i n t e r m e d i a t e i n t h e v a r i o u s r e a c t i o n s , i t w o u l d b e e x p e c t e d t h a t i f I were g e n e r a t e d at a temperature above t h a t a t w h i c h i t is stable, the concentration of I w o u l d be n e g l i g i b l e a n d no c o u p l i n g p r o d u c t ( I V ) s h o u l d b e d e t e c t e d . T h i s has been v e r i f i e d b y a d d i n g b u t y l l i t h i u m t o a m i x t u r e of f u r a n a n d a n o-bromohalobenzene a t temperatures c o n s i d e r a b l y h i g h e r t h a n those a t w h i c h t h e s t a b i l i t y o f I has b e e n w e l l e s t a b l i s h e d . F o r e x a m p l e , w h e n b u t y l l i t h i u m is a d d e d t o a m i x t u r e o f o - b r o m o c h l o r o b e n z e n e a n d a l a r g e excess o f f u r a n , o n l y I I I has been i s o l a t e d . N o acids w e r e f o u n d t o b e p r e s e n t . T h e same w a s t r u e f o r t h e fluoro a n d b r o m o i s o m e r s , a l t h o u g h i n t h e l a t t e r case t h e results a r e n o t as s i g n i f i c a n t as f o r t h e f o r m e r t w o . O r g a n o l i t h i u m compounds other t h a n b u t y l l i t h i u m have been found equally s u i t able i f n o t s o m e w h a t s u p e r i o r f o r g e n e r a t i n g t h e r e a c t i v e species I I a t m o d e r a t e t e m p e r a t u r e s . A 7 5 % y i e l d o f I I I has been o b t a i n e d w i t h p h e n y l l i t h i u m , w h i l e w i t h m e t h y l l i t h i u m y i e l d s u p t o 8 4 % o f I I I h a v e b e e n i s o l a t e d . T h i s i s s u r p r i s i n g because, i n t h e p a s t , m e t h y l l i t h i u m has been f o u n d v e r y ineffective i n h a l o g e n - m e t a l i n t e r c o n version reactions. M e t h y l l i t h i u m interconverts only w i t h v e r y reactive halides such as o - b r o m o a n i s o l e . P h e n y l l i t h i u m i s g e n e r a l l y m o r e effective b u t has t h e d i s a d v a n t a g e of o c c a s i o n a l l y p a r t i c i p a t i n g i n side r e a c t i o n s (27). T h e u n u s u a l effectiveness i n t h i s case m a y b e a t t r i b u t e d t o t h e f o r m a t i o n o f t h e h i g h l y r e a c t i v e i n t e r m e d i a t e , I I . I n order t o substantiate t h a t a halogen-metal interconversion reaction was t h e i n i t i a l step i n t h e r e a c t i o n b e t w e e n o - b r o m o c h l o r o b e n z e n e a n d p h e n y l l i t h i u m , t h e l a t t e r c o m p o u n d was synthesized f r o m iodobenzene a n d l i t h i u m . R e c o v e r y of b r o m o b e n zene i n a g o o d y i e l d s u p p o r t s t h e a b o v e p r o p o s a l . N o a t t e m p t w a s m a d e t o r e c o v e r m e t h y l b r o m i d e w h e n m e t h y l l i t h i u m was u s e d . N o r e a c t i o n o c c u r r e d b e t w e e n o - d i c h l o r o b e n z e n e a n d b u t y l l i t h i u m i n t h e presence of f u r a n . C a r b o n a t i o n , a f t e r s t i r r i n g a t r o o m t e m p e r a t u r e f o r 1 h o u r , afforded o n l y 2 - f u r o i c a c i d . I t is c o n c e i v a b l e t h a t c o n d i t i o n s m i g h t be v a r i e d so as t o effect a r e a c t i o n , as t h e r e is evidence t h a t a r e a c t i o n o c c u r s b e t w e e n b u t y l l i t h i u m a n d o - d i c h l o r o b e n z e n e i n t h e absence o f f u r a n . R e c e n t r e l a t e d w o r k c a n b e c o r r e l a t e d w i t h t h e results j u s t m e n t i o n e d t o g e t h e r w i t h p r e v i o u s findings (9). I n t h e r e l a t e d w o r k , 2 , 2 ' - d i i o d o b i p h e n y l has b e e n p o s t u l a t e d as a n i n t e r m e d i a t e i n t h e r e a c t i o n o f o - d i i o d o b e n z e n e w i t h b u t y l l i t h i u m a n d l i t h i u m i n n o n p o l a r s o l v e n t s (25). I t i s u n l i k e l y t h a t o - i o d o p h e n y l l i t h i u m w o u l d b e p r e s e n t as s u c h i n a n y a p p r e c i a b l e c o n c e n t r a t i o n i n v i e w o f t h e i n s t a b i l i t y o f o - b r o m o p h e n y l l i t h i u m a t — 1 1 0 ° , a n d e s p e c i a l l y because a r e f l u x i n g m i x t u r e o f benzene a n d p e t r o l e u m e t h e r ( b o i l i n g p o i n t , 40° t o 6 0 ° ) w a s e m p l o y e d . Since the o-diiodobenzene w a s a d d e d t o b u t y l l i t h i u m , a n i n t e r m e d i a t e s u c h as 2 - i o d o - 2 - l i t h i o b i p h e n y l w o u l d b e expected t o react further w i t h b u t y l l i t h i u m t o give 2 , 2 - d i l i t h i o b i p h e n y l . T h e latter, i n t u r n , could interact w i t h t w o equivalents of I I t o give 2,2'-bis- ( o - l i t h i o p h e n y l ) - b i /

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p h e n y l . T h i s c o m p o u n d could p a r t i a l l y couple w i t h b u t y l iodide, formed d u r i n g the interconversion reaction, t o give 2,2 -bis- ( o - n - b u t y l p h e n y l ) - b i p h e n y l . A l k y l iodides are m o r e p r o n e t o b e i n v o l v e d i n c o u p l i n g r e a c t i o n s t h a n are o t h e r h a l i d e s . F o r e x a m p l e , m e t h y l i o d i d e couples w i t h 1 - n a p h t h y l l i t h i u m t o g i v e a g o o d y i e l d o f 1 - m e t h y l n a p h t h a l e n e (IS). T h e r e m a i n i n g o r g a n o d i l i t h i u m c o m p o u n d w o u l d g i v e t h e c o r r e sponding acid after carbonation. /

W h e n l i t h i u m i n t e r a c t e d w i t h o-diiodobenzene t h e m a j o r p r o d u c t w a s t r i p h e n y l e n e . T h i s is n o t too s u r p r i s i n g , as i t i s possible t h a t i n t h i s case t h e i n t e r m e d i a t e , 2 - i o d o - 2 ' l i t h i o b i p h e n y l , w o u l d t e n d t o react p r e f e r e n t i a l l y w i t h I I i n s t e a d o f w i t h l i t h i u m a n d as a r e s u l t one w o u l d get 2 - ( o - i o d o p h e n y l ) - 2 - l i t h i o b i p h e n y l , a t y p e o f m o l e c u l e w h i c h has been s h o w n t o u n d e r g o r e a d i l y r i n g closure t o y i e l d t r i p h e n y l e n e . 2 - C h l o r o - 2 ' - ( t r i p h e n y l s i l y l ) - b i p h e n y l has been p r e p a r e d b y a l l o w i n g a n e t h e r e a l s o l u t i o n of o - c h l o r o p h e n y l l i t h i u m t o w a r m i n t h e presence o f t r i p h e n y l c h l o r o s i l a n e . A s m a l l a m o u n t o f t r i p h e n y l e n e was i s o l a t e d also. T h e f o r m e r c o m p o u n d i s p r o b a b l y formed v i a the organolithium compound ( I V , X = C1). T h e corresponding bromo i s o m e r has b e e n p r e p a r e d i n a less a m b i g u o u s m a n n e r b y m e a n s o f a m o n o - h a l o g e n metal interconversion reaction between 2,2 -dibromobiphenyl a n d b u t y l l i t h i u m , followed b y reaction w i t h triphenylchlorosilane.


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Improved Metalation Procedure for Dibenzofuran. D i b e n z o f u r a n h a s been m e t a l a t e d successfully w i t h v a r i o u s o r g a n o l i t h i u m c o m p o u n d s (18). A c o m p a r a t i v e m e t a l a t i o n s t u d y o f d i b e n z o f u r a n w i t h n - b u t y l l i t h i u m has been c a r r i e d o u t i n d i e t h y l e t h e r , d i - n - b u t y l ether, a n d p e t r o l e u m ether ( b o i l i n g p o i n t 28° t o 3 8 ° ) t o g i v e y i e l d s of 56, 76, a n d 1 % , r e s p e c t i v e l y , o f 4 - d i b e n z o f u r a n c a r b o x y l i c a c i d a f t e r c a r b o n a t i o n o f the m e t a l a t e d p r o d u c t . I n a l l these cases t h e r e a c t i o n m i x t u r e s w e r e r e f l u x e d f o r 4 to 2 4 h o u r s ; t h e y i e l d s o f 4 - d i b e n z o f u r y l l i t h i u m i n c r e a s e d s l i g h t l y w i t h i n c r e a s e d r e fluxing p e r i o d s (δ,16). T h e use of organolithium compounds other t h a n n - b u t y l l i t h i u m g e n e r a l l y results i n s m a l l e r y i e l d s o f 4 - d i b e n z o f u r y l l i t h i u m (5,16,21). 4-Dib e n z o f u r y l l i t h i u m has b e e n d e r i v a t i z e d i n r a t h e r g o o d y i e l d s w i t h o - m e t h y l h y d r o x y l amine a n d oxygen to give the amine a n d h y d r o x y c o m p o u n d , respectively (12,24). A l t h o u g h the y i e l d s o f t h e l a t t e r t w o c o m p o u n d s were h i g h e r t h a n t h a t o f t h e c o r r e sponding carboxylic acid, the conditions f o r p r e p a r i n g the 4 - d i b e n z o f u r y l l i t h i u m were similar. B y u s i n g t e t r a h y d r o f u r a n as t h e s o l v e n t , d i b e n z o f u r a n has b e e n m e t a l a t e d w i t h n - b u t y l l i t h i u m i n yields (83 t o 8 6 % ) higher a n d under conditions m u c h m i l d e r t h a n described previously. T h e n - b u t y l l i t h i u m , prepared i n d i e t h y l ether, was added t o a t e t r a h y d r o f u r a n s o l u t i o n o f d i b e n z o f u r a n a t —60° a n d t h e n t h e r e a c t i o n m i x t u r e w a s stirred between 0 ° a n d 5° f o r 1 hour before carbonating. T e t r a h y d r o f u r a n was p u r p o s e l y selected because i t is a m o r e basic s o l v e n t t h a n a n y u t i l i z e d i n p r e v i o u s s t u d i e s . T h e base s t r e n g t h o f t e t r a h y d r o f u r a n t o w a r d b o r o n t r i f l u o r i d e i s g r e a t e r t h a n t h a t o f d i e t h y l e t h e r (2). T o e x a m i n e f u r t h e r t h e p r o n o u n c e d effect o f t e t r a h y d r o f u r a n o n t h e m e t a l a t i o n o f d i b e n z o f u r a n , a r u n was m a d e a t — 5 0 ° . A s i g n i f i c a n t 1 1 % y i e l d o f a c i d w a s o b t a i n e d a f t e r s t i r r i n g a t —50° f o r 1 h o u r f o l l o w e d b y c a r b o n a t i o n . I n c o n t r a s t , a d i e t h y l e t h e r s o l u t i o n of d i b e n z o f u r a n a n d b u t y l l i t h i u m s t i r r e d a t 0 ° f o r 1 h o u r a f f o r d e d o n l y a 5 % y i e l d of acid. I t was hoped t h a t exclusion of d i e t h y l ether f r o m the reaction m i g h t result i n metalation under even milder conditions t h a n mentioned. F o r this purpose t h e n - b u t y l l i t h i u m was p r e p a r e d in situ a t —25° f r o m b u t y l c h l o r i d e , t o a v o i d loss o f t h e R L i compound. I t has been o b s e r v e d t h a t t h e y i e l d o f b u t y l l i t h i u m decreases m o r e r a p i d l y i n t e t r a h y d r o f u r a n t h a n i n d i e t h y l e t h e r . T h e highest y i e l d o f a c i d o b t a i n e d w i t h t h i s m e t h o d was 3 0 % . T h e use o f b u t y l b r o m i d e i n s t e a d o f b u t y l c h l o r i d e d i d not give higher yields. L i t h i u m Cleavages of Some Heterocycles i n Tetrahydrofuran. C l e a v a g e s o f heterocycles u s i n g v a r i o u s m e d i a a n d c l e a v i n g agents has o f t e n p r o v e d t o b e a v a l u a b l e tool in synthesis a n d structure proof.



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R e f l u x i n g l i t h i u m a n d d i b e n z o f u r a n i n d i e t h y l ether f o r 22 h o u r s afforded excellent y i e l d s o f 3 , 4 - b e n z o c o u m a r i n w h e n t h e r e a c t i o n was t e r m i n a t e d b y c a r b o n a t i o n . W h e n r e f l u x i n g d i o x a n e was used as t h e s o l v e n t , o n l y 2 - h y d r o x y b i p h e n y l w a s o b t a i n e d u p o n h y d r o l y s i s o r c a r b o n a t i o n a f t e r 12 h o u r s (6). D i b e n z o - p - d i o x i n has been c l e a v e d b y l i t h i u m i n r e f l u x i n g d i e t h y l e t h e r (24 h o u r s ) to y i e l d u p o n c a r b o n a t i o n 2 3 % o f 2 - h y d r o x y - 2 ' - c a r b o x y d i p h e n y l e t h e r . T h i s m o l e c u l e could presumably be cleaved i n refluxing dioxane. I n r e f l u x i n g d i e t h y l e t h e r , l i t h i u m does n o t cleave d i b e n z o t h i o p h e n e e v e n a f t e r 36 hours. H o w e v e r , dibenzothiophene can be cleaved b y l i t h i u m i n refluxing dioxane o v e r a p e r i o d of 12 h o u r s t o y i e l d b i p h e n y l a n d 2 - m e r c a p t o b i p h e n y l a f t e r h y d r o l y s i s o r c a r b o n a t i o n (6). T h i s a g a i n d e m o n s t r a t e s t h e d e s t r u c t i v e n a t u r e o f r e f l u x i n g dioxane o n organometallic compounds. A t t e m p t s t o cleave J V - e t h y l c a r b a z o l e w i t h l i t h i u m i n r e f l u x i n g d i o x a n e h a v e r e s u l t e d i n e s s e n t i a l l y q u a n t i t a t i v e r e c o v e r y o f s t a r t i n g m a t e r i a l a f t e r 2 4 h o u r s (11). T h e cleavage w a s n o t a t t e m p t e d i n e t h e r , b u t a n e g a t i v e r e s u l t m a y b e a f a i r l y safe a s s u m p t i o n . C a r b a z o l e g a v e t h e same r e s u l t s u n d e r i d e n t i c a l c o n d i t i o n s . W h e n p u r i f i e d t e t r a h y d r o f u r a n was u s e d , a l l t h e a f o r e - m e n t i o n e d c o m p o u n d s h a v e u n d e r g o n e cleavage w i t h s i g n i f i c a n t ease. I n a l l cases t h e r e a c t i o n s were e x o t h e r m i c , g i v i n g rise t o a d a r k b l u e - g r e e n color. C o l o r test I was u s u a l l y p o s i t i v e w i t h i n 2 m i n u t e s a f t e r the r e a c t a n t s were m i x e d . I n m a n y i n s t a n c e s , t h e d a r k b l u e - g r e e n c o l o r g r a d u a l l y t u r n e d t o a d a r k b r o w n . F o r c o m p a r i s o n p u r p o s e s , t h e r e a c t i o n s were a l l r u n f o r 45 m i n u t e s a n d t h e n e i t h e r h y d r o l y z e d o r c a r b o n a t e d . Dibenzothiophene and dibenzo-p-dioxin reacted completely d u r i n g t h e allotted t i m e . B o t h r e a c t i o n s a p p r o a c h e d t h e reflux t e m p e r a t u r e o f t e t r a h y d r o f u r a n i f t h e y were n o t c o n t r o l l e d . D i b e n z o - p - d i o x i n gave the n o r m a l products u p o n carbonation i n better y i e l d t h a n t h e c o r r e s p o n d i n g d i e t h y l e t h e r cleavage, b u t d i b e n z o t h i o p h e n e p r o d u c e d 3 , 4 - b e n z o t h i o c o u m a r i n a n d t h e disulfide o f 2 - m e r c a p t o - 2 - c a r b o x y b i p h e n y l . T h e s e are p r o b a b l y formed f r o m the 2-mercapto-2 -carboxybiphenyl d u r i n g the w o r k - u p . A small amount of b i p h e n y l was also o b t a i n e d f r o m t h e u n c o n t r o l l e d r e a c t i o n s of d i b e n z o t h i o p h e n e . A m a x i m u m y i e l d of cleavage p r o d u c t s was r e a l i z e d a t 2 5 ° f o r d i b e n z o t h i o p h e n e a n d d i b e n z o - p - d i o x i n , u s i n g a n ice b a t h t o m o d e r a t e t h e r e a c t i o n s . I n t h e case o f d i b e n z o f u r a n , i t was best t o use a h i g h e r t e m p e r a t u r e , because a 7 5 % r e c o v e r y of s t a r t i n g m a t e r i a l r e s u l t e d a t 2 5 ° . T h e u n c o n t r o l l e d r e a c t i o n s w h i c h w a r m e d u p t o 40° t o 50° g a v e a 2 0 % y i e l d o f 3 , 4 - b e n z o c o u m a r i n a f t e r c a r b o n a t i o n . C l e a v a g e o f t h i a n t h r e n e a t 25° w i t h l i t h i u m y i e l d e d n o i d e n t i f i a b l e p r o d u c t s , b u t 9 0 % o f t h e s t a r t i n g m a t e r i a l was i n t h e f o r m o f a n u n p l e a s a n t s m e l l i n g a c i d i c o i l a f t e r c a r b o n a t i o n . T h i s evidence p l u s t h e fact t h a t color test I was p o s i t i v e c a n b e r e c o n c i l a b l e o n l y w i t h cleavage o f t h i s h e t e r o c y c l e . W h e n u s i n g r e f l u x i n g d i e t h y l e t h e r as t h e s o l v e n t , 7 2 % o f t h i a n t h r e n e was r e c o v e r e d , e v e n t h o u g h color test I was p o s i t i v e after 1 hour. N o p r o d u c t s h a v e been i d e n t i f i e d f r o m t h e l i t h i u m cleavage of J V - e t h y l e a r b a z o l e i n t e t r a h y d r o f u r a n . S o m e cleavage m u s t h a v e o c c u r r e d , as o n l y 7 5 % of t h e s t a r t i n g m a t e r i a l was r e c o v e r e d a f t e r 45 m i n u t e s of r e f l u x i n g a n d c o l o r test I was p o s i t i v e . T h e i n f r a r e d s p e c t r a of some o f t h e r e c o v e r e d oils s h o w e d a n N - H b a n d . L i t h i u m i n r e fluxing t e t r a h y d r o f u r a n f o r 45 m i n u t e s f a i l e d t o cleave c a r b a z o l e , g i v i n g a 9 0 % r e c o v e r y of s t a r t i n g m a t e r i a l . W h i l e d i b e n z o f u r a n c l e a v e d r a t h e r e a s i l y i n e t h e r , d i b e n z o t h i o p h e n e resisted c l e a v age u n d e r these c o n d i t i o n s . H o w e v e r , i n t e t r a h y d r o f u r a n , d i b e n z o t h i o p h e n e gave t h e best y i e l d o f cleavage p r o d u c t a t 2 5 ° , whereas d i b e n z o f u r a n was a p p r e c i a b l y c l e a v e d only a t higher temperatures. A n o t e w o r t h y d e v i a t i o n f r o m h e t e r o c y c l e s was t h e cleavage o f d i p h e n y l e t h e r t o y i e l d phenol, benzoic a c i d , a n d 2 - c a r b o x y d i p h e n y l ether after carbonation. T h e last p r o d u c t m a y b e a c c o u n t e d for b y a s s u m i n g m e t a l a t i o n o f the d i p h e n y l e t h e r b y p h e n y l l i t h i u m o b t a i n e d b y cleavage of the d i p h e n y l e t h e r . /

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OILMAN—ORGANOMETALLIC COMPOUNDS

7

C o u p l i n g Reactions with Some Organolithium Compounds i n Tetrahydrofuran. D e p e n d i n g u p o n c o n d i t i o n s a n d solvents u s e d , a v a r i e t y o f p r o d u c t s h a v e been o b tained f r o m reactions of dihalobenzene compounds w i t h n - b u t y l l i t h i u m . One i n v e s t i g a t i o n (25) d e s c r i b e d t h e r e a c t i o n s of o - d i i o d o b e n z e n e a n d o - d i b r o m o b e n z e n e w i t h m a g n e s i u m , l i t h i u m , a n d n - b u t y l l i t h i u m i n v a r i o u s s o l v e n t s t o y i e l d a series of c o u p l i n g p r o d u c t s . T h e f o r m a t i o n of these c o u p l i n g p r o d u c t s i n the reactions i n v o l v i n g o - d i i o d o benzene has been p o s t u l a t e d t o p r o c e e d t h r o u g h t h e i n i t i a l f o r m a t i o n of 2 , 2 ' - d i i o d o b i p h e n y l as a n i n t e r m e d i a t e . H o w e v e r , n e i t h e r 2 , 2 - d i i o d o b i p h e n y l n o r 2 , 2 ' - d i b r o m o b i p h e n y l c o u l d be i s o l a t e d f r o m t h e r e a c t i o n m i x t u r e s . /

A n o t h e r i n v e s t i g a t i o n (9) d e s c r i b e d the reactions of o - d i b r o m o b e n z e n e , o-chlorobromobenzene, a n d o-fluorobromobenzene w i t h n - b u t y l l i t h i u m i n ethereal solution a t low t e m p e r a t u r e s t o y i e l d u p o n c a r b o n a t i o n o - b r o m o b e n z o i c , o - c h l o r o b e n z o i c , a n d o-fluorobenzoic acids, r e s p e c t i v e l y . W h e n t h e r e a c t i o n m i x t u r e s w e r e w a r m e d p r i o r to c a r b o n a t i o n , t h e v a r i o u s o - h a l o p h e n y l l i t h i u m reagents u n d e r w e n t c o u p l i n g r e a c t i o n s to y i e l d s u c h p r o d u c t s as 2 - h a l o - 2 - l i t h i o b i p h e n y l , 2 - ( o - h a l o p h e n y l ) - 2 M i t h i o b i p h e n y l , a n d t r i p h e n y l e n e . H o w e v e r , i n no case was a n y 2 , 2 ' - d i h a l o b i p h e n y l i s o l a t e d . 7


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A d d i t i o n a l w o r k has s h o w n t h a t one e q u i v a l e n t o f a n e t h e r e a l s o l u t i o n of n - b u t y l l i t h i u m reacts i n s t a n t a n e o u s l y a t —78° w i t h t w o e q u i v a l e n t s o f o - d i b r o m o b e n z e n e , d i s s o l v e d i n t e t r a h y d r o f u r a n , t o g i v e , as t h e m a i n p r o d u c t , 2 , 2 - d i b r o m o b i p h e n y l i n y i e l d s r a n g i n g f r o m 67 t o 7 4 % . Similarly, when p-dibromobenzene and p-chlorob r o m o b e n z e n e were d i s s o l v e d i n t e t r a h y d r o f u r a n a n d t r e a t e d w i t h a n e t h e r e a l s o l u t i o n of n - b u t y l l i t h i u m i n a 2 t o 1 r a t i o , t h e r e r e s u l t e d 4 , 4 - d i b r o m o b i p h e n y l a n d 4 , 4 ' - d i c h l o r o b i p h e n y l , r e s p e c t i v e l y . H o w e v e r , the y i e l d s of the l a t t e r t w o c o m p o u n d s were m u c h l o w e r t h a n t h a t of 2 , 2 ' - d i b r o m o b i p h e n y l . A l t h o u g h t h e m e c h a n i s m o f t h e r e a c t i o n i n t e t r a h y d r o f u r a n has n o t been e x t e n s i v e l y s t u d i e d , i t i s c o n c e i v a b l e t h a t o - b r o m o p h e n y l l i t h i u m i s f o r m e d as a n i n t e r mediate v i a a halogen-metal interconversion reaction between o-dibromobenzene a n d n - b u t y l l i t h i u m , a n d t h a t t h i s i n t u r n c a n c o u p l e w i t h o - d i b r o m o b e n z e n e t o g i v e the final p r o d u c t , 2 , 2 - d i b r o m o b i p h e n y l . F r o m the f o r e g o i n g d i s c u s s i o n , t h e r e i s a s t r o n g inference t h a t t h e s o l v e n t m a y p l a y a n i m p o r t a n t role i n the r e a c t i o n of n - b u t y l l i t h i u m w i t h a d i h a l o b e n z e n e c o m p o u n d . I n f u r t h e r s u p p o r t o f t h i s c o n c l u s i o n , i t has been f o u n d t h a t w h e n o - d i b r o m o benzene i n t e r a c t s w i t h n - b u t y l l i t h i u m i n d i e t h y l e t h e r u n d e r i d e n t i c a l c o n d i t i o n s a n d w i t h the same q u a n t i t i e s o f r e a c t a n t s e m p l o y e d i n t h e r u n c a r r i e d o u t i n t e t r a h y d r o f u r a n , n o 2 , 2 - d i b r o m o b i p h e n y l was i s o l a t e d . T h e o n l y p r o d u c t s were a n u n i d e n t i f i e d e t h e r - i n s o l u b l e m a t e r i a l a n d a h i g h l y viscous o i l . p-Chlorobromobenzene a n d p-dibromobenzene, when reacted w i t h n - b u t y l l i t h i u m i n d i e t h y l ether, undergo a n o r m a l halogen-metal interconversion reaction t o give p - c h l o r o p h e n y l l i t h i u m a n d p - b r o m o p h e n y l l i t h i u m , r e s p e c t i v e l y , i n h i g h y i e l d s (13). H o w e v e r , i t is apparent t h a t the mode of reaction is changed w h e n t e t r a h y d r o f u r a n is used as t h e s o l v e n t . T h i s p r e p a r a t i o n o f 2 , 2 ' - d i b r o m o b i p h e n y l i s i n t e r e s t i n g also f r o m a s y n t h e t i c v i e w p o i n t , as p r e v i o u s t o t h i s , t h e o n l y s a t i s f a c t o r y m e a n s for p r e p a r i n g 2 , 2 ' - d i b r o m o b i p h e n y l was a m u l t i s t e p process i n v o l v i n g d i a z o t i z a t i o n of 2 , 2 ' - d i a m i n o b i p h e n y l (4,35). T h e p r o c e d u r e j u s t d e s c r i b e d offers s e v e r a l a d v a n t a g e s o v e r the o l d e r m e t h o d s . T h e o v e r - a l l y i e l d i s p r o b a b l y h i g h e r , t h e r e are fewer steps i n v o l v e d , a n d t h e r e a c t i o n c a n be a c h i e v e d r a p i d l y . T h i s r e a c t i o n i s n o w f i n d i n g extensive use for the p r e p a r a t i o n of 2 , 2 ' - d i b r o m o b i p h e n y l , w hich is a n i m p o r t a n t i n t e r m e d i a t e i n the p r e p a r a t i o n o f some c y c l i c o r g a n o s i l i c o n c o m p o u n d s (8). /

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r

Effect of Solvent on Course of Carbonation Reaction of 2-Quinolyl- and 1-Isoquinolyllithium. I n a recent s p l e n d i d i n v e s t i g a t i o n , N o r m a n t (32) f o u n d t h a t e x c e l l e n t y i e l d s o f the G r i g n a r d reagents c o u l d b e o b t a i n e d w i t h a l k e n y l a n d a r y l c h l o r i d e s b y e m p l o y i n g t e t r a h y d r o f u r a n as t h e s o l v e n t . T h i s s o l v e n t has b e e n u s e d f u r t h e r t o include the p r e p a r a t i o n of p h e n y l l i t h i u m f r o m chloro- a n d fluorobenzene (33) w i t h



8


lithium wire, and 2-quinolyllithium from 2-bromoquinoline by means of a halogen-metal interconversion reaction with n-butyllithium at —60°. On carbonating 2-quinolyllithium, which was prepared in tetrahydrofuran, by pouring jetwise onto a slurry of dry ice-tetrahydrofuran, the 2-quinolinecarboxylic acid was obtained in a yield of 50%. The same intermediate, however, when made in diethyl ether and carbonated by employing a dry ice-ether slurry, yields 2,2'-diquinolyl ketone in 20% yield and no acid. When this intermediate in diethyl ether was carbonated at —100°, both acid and ketone were obtained. Ketone formation on carbonation of organolithium derivatives has been noted {22). This reaction has been shown to involve the initial formation of the carboxylic salt which is again attacked by the organolithium reagent (1). The intermediate was found to be the dilithio ketal, which resisted further substitution or loss of lithium oxide. As the stability of the ketal was shown to be enhanced by the presence of electronattracting groups (87), the electrostatic effect of the nitrogen atom can be considered to have been involved in the stabilization of the quinolyl ketal. Further evidence in support of this hypothesis was the isolation of only the acids on carbonation of 3quinolyl- and 4-isoquinolyllithium under the same conditions. The greater basicity and solvating effect of tetrahydrofuran may have been responsible for reducing the effective formation of the intermediate ketal which would result in the production of the acids in preference to the ketones. 2-Quinolyl- and 1-isoquinolyllithium have been prepared for the first time. The general procedure used was a low temperature halogen-metal interconversion reaction with n-butyllithium. Each of these organolithium compounds was characterized by a reaction with benzophenone to give the corresponding tertiary alcohols. 3-Quinolyllithium was reported earlier (20), and 2-quinolylmagnesium bromide has been prepared with difficulty and in low yield (89). Incidental to other interesting effects of tetrahydrofuran as a solvent, mention should be made of the following. First, an R S i H compound reacts with R L i , but not with R M g X , in diethyl ether to give R S i types; however, the Grignard reagent does undergo a related reaction in tetrahydrofuran. Second, tetrahydrofuran is not only a good solvent for reactions involving sparingly soluble organosilicon and organogermanium compounds, but also improves numerous reactions of these and related types. For example, the cleavage of hexaaryldisilanes and hexaaryldigermanes by lithium to give R M L i types is much more effectively carried out in tetrahydrofuran. Also, hexaethyldisilane reacts with lithium in tetrahydrofuran. Third, in the reaction of o-dibromobenzene with allylmagnesium chloride in tetrahydrofuran there are formed, subsequent to carbonation, significant quantities of o-allylbenzoic acid. Details will be presented on the preparation of R L i compounds for R F , RC1, and R B r compounds in tetrahydrofuran, and their stabilities in this and some other solvents. 3

4

3

Acknowledgment Grateful acknowledgments are made to Ernest A . Zuech, Glen D . Lichtenwalter, and Mark B . Hughes. Credit for experimental data on newer studies of organometallic compounds included in this paper belongs to Richard D . Gorsich, Donald L . Esmay, Theodore S. Soddy, Joseph J . Dierich, and Bernard J . Gaj. The author is indebted for financial assistance for part of this work, particularly to the M a terials Laboratory, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio; and to the Division of Biology and Medicine, United States Atomic Energy Commission. Literature Cited (1) Bluhm, H . F., Donn, H . V., Zook, H . D., J. Am. Chem. Soc. 77, 4406 (1955). In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

GILMAN—ORGANOMETALLIC COMPOUNDS (2) (3) (4) (5) (6) (7) (8)

9

Brown, H . C., Adams, R. M., Ibid., 64, 2557 (1942). Bunnett, J. F., Zahler, R. E., Chem. Revs. 49, 273 (1951). Dobbie, J. J., Fox, J. J., Gauge, A. J. H., J. Chem. Soc. 99, 684 (1911). Gilman, H., Benkeser, R. Α., Dunn, G. E., J. Am. Chem. Soc. 72, 1689 (1950). Gilman, H., Esmay, D., Ibid., 75, 2947 (1953). Gilman, H., Fury, M., Ibid., 50, 1214 (1928). Gilman, H., Gorsich, R. D., Ibid., 77, 6380 (1955).

(9) Ibid., 78, 2217 (1956).


(10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34)

Gilman, H., Haubein, A.H.,Ibid., 66, 1515 (1944). Gilman, H., Honeycutt, J. B., Jr., Ingham, R., J. Org. Chem. 22, 388 (1957). Gilman, H., Ingham, R. K., J. Am. Chem. Soc. 75, 4843 (1953). Gilman, H., Langham, W., Moore, F. W., Ibid., 62, 2327 (1940). Gilman, H., Meyers, C. H., J. Ind. Eng. Chem. 14, 243 (1922) ; 15, 61 (1923). Gilman, H., Moore, F. W., J. Am. Chem. Soc. 62, 1843 (1940). Gilman, H., Moore, F. W., Baine, O., Ibid., 63, 2479 (1941). Gilman, H., Moore, F. W., Jones, R. G., Ibid., 63, 2482 (1941). Gilman, H., Morton, J. W., Jr., "Organic Reactions," Vol. VIII, Chap. 6, Wiley, New York, 1954. Gilman, H., Schulze, F., J. Am. Chem. Soc. 47, 2002 (1925). Gilman, H., Spatz, S. M., Ibid., 63, 1553 (1941). Gilman, H., Stuckwisch, C. G., Ibid., 67, 877 (1945). Gilman, H., Van Ess, P. R., Ibid., 55, 1258 (1933). Gilman, H., Wilkinson, P. D., Fishel, W. P., Meyers, C. H., Ibid., 45, 150 (1923). Gilman, H., Young, R. V., Ibid., 57, 1121 (1935). Heaney, H., Mann, F. G., Millar, I. T., J. Chem. Soc. 1956, 1, 4692. Hine, J., "Physical Organic Chemistry" pp. 453-61, McGraw-Hill, New York, 1956. Jones, R. G., Gilman, H., "Organic Reactions," Vol. VI, p. 343, Wiley, New York, 1951. Kohler, E . P., Richtmyer, N . K., J. Am. Chem. Soc. 52, 3736 (1930). Kohler, E. P., Stone, J. F., Fuson, R. C., Ibid., 49, 3181 (1927). Marvel, C. S., Gauerke, C. G., Hill, E. L., Ibid., 47, 3009 (1925). Morton, Α. Α., J. Org. Chem. 21, 593 (1956). Normant, H., Compt. rend. 239, 1510 (1954). Oita, K., doctoral dissertation, Iowa State College, Ames, Iowa, March 1955. Roberts, J. D., Semenow, D. Α., Simmons, Η. E., Jr., Carlsmith, L. Α., J. Am. Chem. Soc. 78, 601 (1956).

(35) Schwechten, H.-W., Ber. 65, 1605 (1932) (36) Siggia, S., "Quantitative Organic Analysis Via Functional Groups," p. 48, Wiley, New York, 1949. (37) Tegner, C., Acta Chem. Scand. 6, 782 (1952). (38) Tschugaeff, L., Ber. 35, 3912 (1902).

(39) Wibaut, J. P., Herrings, L. G., Rec. trav. chim. 74, 1003 (1955). (40) Wittig, G., Herwig, W., Ber. 87, 1511 (1954). (41) Wittig, G., Pohmer, L., Angew. Chem. 67, 348 (1955). (42) Zerewitinoff, T., Ber. 40, 2023 (1907).

RECEIVED for review May 10, 1957. Accepted June 1, 1957.


Organometallic Compounds

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