June 5 , 1958
CLEAVAGE-CYCLIZATION OF SILICON-CONTAINING ORGANOLITHIUMS
2677
ORGANIC A N D BIOLOGICAL CHEMISTRY [CONTRIBUTIOSFROM THE CHEMICAL LABORATORY O F IOWA STATE COLLEGE]
An Intramolecular Cleavage-Cyclization Reaction of Silicon-containing Organolithium Compounds B Y DIETRLIR
IX7ITTENBERG AND
HENRYGILMAN
RECEIVED DECEMBER 23, 1957 The reaction of chlorotriphenylsilane with tetramethylenedilithiurn gave thc expected tetr,imctliS.leiie-bis-( tripheiiylsilane) only in very low yields, while as the main products 1,l-diphenylsilacyclopentaneand tctraphenylsilane were obtained. The formation of these compounds by an intramolecular cleavage-cyclization reaction of the reaction intermediate 4-triphenylsilyl-butyllithium is discussed. 4-Bromobutyltriphenylsilane was prepared in a three-step synthesis and allowed t o react with lithium and magnesium. The stability of these organometallic compounds was studied. The investigation was further extended to the reaction of chlorotriphenylsilane and pentamethylenedilithium.
A number of studies concerned with the prep- tetramethylenedilithium and chlorotriphenylsilane aration of silicon-containing ring systems, in in diethyl ether, we found the desired product to which silicon is bonded only to carbon, have been be formed only in a 4.475yield. The unexpected reported.la-m The reaction of difunctional Grig- main products were 1,l-diphenylsilacyclopentane nard reagents with silicon tetrachloride has been (IV) and tetraphenylsilane (V), which were isolated applied in the syntheses of 1,l-dichlorosilacyclo- in 38.7 and 4870 yields, respectively. alkanes.la-f As an example 1,l-dichlorosilacyclo( C6H5)3SiC1 Li( CH2)aLi -+- ( C6H&Si(CH2)dLi hexane was formed in a 70y0yield from the reaction I I1 of 1,5-pentamethylenedimagnesiumdibrornide and silicon tetrachloride. Difunctional lithium comJ.+I pounds similarly yielded spirans with silicon as the CHzCH, $/ ( C G & ) ~ S ~ ( C HC6H5)3 ~)~S~( spiro atom.ldjgjk,l Treatment of appropriately 111 substituted trichlorosilanes with difunctional Grignard reagents provided a useful route to the syn- (C6Hs)aSi \ +I thesis of monofunctional cyclic organosilicon comI V CHlCIIz C&Li ---+(C6H5)4Si (T) pounds. By this procedure, for instance, l-chloroApparently tetramethylenedilithium first dis1-methyl- and 1-chloro-1-phenylsilacyclopentane places the chlorine atom in chlorotriphenylsilane to were obtained in yields of 47 and 36y0, respectively, form 4-triphenylsilyl-butyllithium (11). The latfrom the reaction of 1,4-tetrarnethylenedimagne- ter in a slow reaction couples with a second niolesium dibromide and trichloromethylsilane and tri- cule of chlorotriphenylsilane to give 111. But in a chlorophenylsilane, respectivelyU2 Several “non- more rapid intramolecular cleavage-cyclization refunctional” cyclic organosilicon compounds were action I1 splits off p h e n y l l i t h i ~ mt6 ~ form 1V. obtained from a difunctional Grignard reagent Phenyllithium thereafter couples with rhlorotriand a disubstituted dichlorosilanele under forced phenylsilane to give tetraphenylsilane. conditions, but difunctional lithium compounds apThe two compounds I11 and IV, which have not parently give much better resultslc,d,g,kJ,mand been reported previously, were both synthesized react more readily. by independent methods. Tetraniethylene-hisThe reaction of difunctional organolithiuiri com- (triphenylsilane) was formed in a 3% yield from pounds with trisubstituted chlorosilanes has been the reaction of 1,4dibromobutane with triphenylreported to yield “non-functional’’ disilanes. Thus silyllithium in tetrahydrofuran. As a main prodtetra-, penta-, hexa- and octamethylene-bis-(tri- uct hexaphenyldisilane was isolated in a 74y0 methylsilane) were obtained from the correspond- yield, formed apparently by a halogen-metal intering dilithiuin compounds and chlorotrimethyl- conversion reacti0n.j 1 , 1-Diphenylsilacyclopensilane in 63, 68, 42 and 71y0 yields, re~pectively.~ tane was obtained in a 46% yield from the reaction I n attempts to prepare tetramethylene-bis-(tri- of dichlorodiphenylsilane with tetramethylenediphenylsilane) (111) from the analogous reaction of lithium. (1) (a) A. Bygden, B e y . , 48, 1236 (1915); (b) J. M. Hersch, U. S. I n order to throw light on the abnormal cleavage Patent 2,464,231 [C. A , , 43, 8210 (1949)l; (c) R . m‘est and E. G , cyclization reaction, 4-bromobutyl-triphenylsilane Rochow, Natrcrwissenschaften, 40, 142 (1953); (d) R. West, THIS was synthesized, allowed to react with lithium and JOURNAL, 76, 6012 (1954); (e) M. Kumada, J . I?ks:. Polytech. Osaka magnesium, and the stability of the organometallic City Univ., Ser. C, 1, 11 (1951) IC. A , , 46, 6082 (1952)l; (f) A. F. Plate, N. A. Monna and Yu. P. Egorov, Doklady. Akad. Narck S.S.S.R., 97,847 compounds of type I1 was investigated. (1954) [C. A . , 49, 10169 (1955)l; (g) A. F. Plate, N. A. Belikova and Wittig and Rueckert6 reported the cleavage of Yu. P.Egorov, Isrest. Akad. Nattk S.S.S.R., Otdel. K h i m . Nauk, 1085 tetrahydrofuran by triphenylmethylsodium a t room (1856) IC. A . , 61, 5085 (195711; (h) L. H. Sommer and 0. F. Bennett,
+
/
’I
THISJOURNAL, 79, 1008 (1957); (i) L. H. Sommer and G. A. Baum, ibid., 76, 5002 (1954); (j) R. West, ibid., 7 7 , 2339 (1955); (k) K. Oita and H. Gilman, ibid., 79, 339 (1957); (I) K. Oita and H. Gilman, J . Or Chem., 12, 336 (1957); (m) H. Gilman a n d R. D. Gorsich, THISJOURNAL, 77, 6380 (1955). (2) H. Gilman and G. D. Lichtenwalter, unpublished studies on alicyclic silicon compounds. (3) R. West and E. G. Rochow, J . Org, Chem., 18, l i 3 9 (1953).
.
+
(4) Apparently no phenyllithium is split off, however, when nbutyltriphenylsilane is treated with n-butyllithium; see H. Gilman. R. A. Benkeser and G. E. D u m , THISJOURNAL,71, 5878 (1950). ( 5 ) For halogen-metal interconversion in silicon chemistry see A. G . Brook, H. Gilman and L. S . Miller, ?bid., 76, 4759 (1953); A. G, Brook and S . Wolfe, ibid., 79, 1431 (1957); H. Gilman and D. H. Miles, ibid., 80, 611 (1958). (6) G. Wittig and A. Rueckert, Liebigs A n n . Chem., 666, 104 (1950).
2678
Vol. 80
DIETMAR WITTENBERG AND HENRYGILMAN
temperature in the presence of triphenylboron to give a boron complex salt, the hydrolysis of which yielded 5,5,5-triphenyl-l-pentanol (VI). They also reported that triphenylmethylsodium itself did not cleave the cyclic ether, even after prolonged heating at 100'. (C&s)sCNa
+ C4HsO + (CsH&B +
[(CeHs)3C(CH~)40~B(CgHg)3] --Na (CsHs)K(CHz)40H VI
+ acid
+
---+
Normant7 found that Grignard reagents cleave tetrahydrofuran a t 200' to give primary alcohols of the type R-(CHZ)dOH. Gorsich* has obtained 4hydroxybutyltriphenylsilane (VII), the silicon analog of VI, in an lSy0 yield on refluxing triphenylsilyllithium in tetrahydrofuran for 2.7 days. To improve the yield the cleavage reaction was carried out in a sealed tube, which was heated for 3 hours at 125'. Color Test I9 was found to be negative and from the reaction mixture VI1 was isolated in a 71% yield. The alcohol VI1 was converted to the bromide VI11 with phosphorus tribromide'o in a 54.5% yield. (CeH6)aSiLi -+- ( C5H6)&(CH2)rOH CaHaO VI1
+
+ PBra
___f
(C6€1~)3Si( CH&Br
11
VI11 f Mg
1
CHzCHz (c&),$
\CHr
\
/
'---+I
JL
+ C&,Li
(C&,),si( CHz)rSi(CeHo)a
+ I
SI11 XIV CH2CHz +( C & , ) 8 While other ring closure reactionslcId show maximum yields in the preparation of six-membered cyclic silanes, slightly lower yields with fivemembered rings and very low yields with the sevenmembered rings, the cleavage-cyclization reaction seems to occur preferably when a five-membered cyclic silane is formed as a reaction product. A similar abnormal cyclization was observed recently in the dibenzosilole series.'' On treatment of 5chloro-5methyldibenzosilole (XV) with an equimolar quantity of 2,2'-dilithiobiphenyl in diethyl ether almost equimolar amounts of 5,5'-spirobi(dibenzosilole) (XVI) and 5,5-dimethyldibenzosilole (XVII) were obtained.
f [( CsHs)aSi(CHz)rIXO X
(C6H&Si( CH&OOH IX
t
a 60% yield, together with 20% of coupling product, octamethylene-bis-(triphenylsilane)(XII). The investigation was further extended to the reaction of chlorotriphenylsilane and pentamethylenedilithium. I n this case, however, the normal coupling product pentamethylene-bis-(triphenylsilane) (XIII) was obtained in a 75% yield. As a by-product 0.65% of tetraphenylsilane and some impure 1,l-diphenylsilacyclohexane (XIV) was isolated.
I
L1
1, f C O 2 2, +HzO
+ YlII
II
I
+
--+ (C&5)3Si( CHz)&fgBr --+XI (C6H&Si( C&)&(c6&)3 XI1
When 4-bromobutyltriphenylsilane was treated with lithium in ethyl ether a t -25' and the mixture carbonated as soon as it had warmed to room temperature, benzoic acid, benzophenone and 1,ldiphenylsilacyclopentane (IV) were isolated in 56.5, 20 and 50.6% yields, respectively. 4-Carboxybutyltriphenylsilane (IX) was not formed under these conditions. When 4-triphenylsilyl-butyllithium (11) prepared a t -23' was carbonated a t low temperatures, however, IX was isolated in a 5670 yield, together with a small amount of 1,9bis-(triphenylsilyl)-5-nonanone (X). Benzoic acid and the cyclic compound IV were found only in trace amounts. The reaction of 4-bromobutyl-triphenylsilane (IX) with magnesium in ether a t reflux temperature gave after carbonation the normal acid IX in (7) H. N o r m a n t , C o m p f . rend., 239, 1510 (1954). (8) R. D. Gorsich, unpublished studies. (9) H. Gilman a n d F. Schulze. THISJOURNAL,47, 2002 (1925); G. Wittig, Angew. Chem., 53, 243 (1940). (10) Modification of the method of L. H. Sommer, R. E. Van Strien a n d F. C. Whitmore, THISJOURNAL,71, 3056 (1919).
XVII
/ \
CH3 CH3
Experimental Tetramethylenedilithium and Chlorotriphenylsi1ane.Tetramethylenedilithium was prepared according to the directions of West and Rochow.8 Twenty-one and sixtenths grams (0.1 mole) of 1,4-dibrornobutane in 150 nil. of anhydrous ether was added slowly with vigorous stirring t o 5.0 g. (0.72 g. atom) of lithium sand, suspended in 50 ml. of ether. The reaction was started by stirring for a few minutes a t room temperature; the mixture thereafter was kept at -10 to -20". After the addition was completed, the run was stirred for 1 hr. a t -10' and 0.5 hr. a t 10". The solution was filtered through glass wool into an addition funnel. The tetramethylenedilithium solution was then slowly added with stirring t o 55 g. (0.187 mole) of chlorotriphenylsilane in 50 ml. of anhydrous ether. The reaction mixture was stirred for one hr. a t -lo', then allowed to warm to room temperature. Three hours later Color Test I 9 was negative. The white precipitate was filtered and (11) H. Gilman and I
