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Oxidations with Peroxytrifluoracetic Acid-Boron Fluoride HAROLD HART, CHARLES A. BUEHLER, and ANTHONY J . WARING Michigan
State University,
East Lansing,
Mich.
Peroxytrifluoroacetic acid-boron fluoride pro vides a potent, versatile, and selective oxidant, particularly for aromatic systems.
The reagent
can be thought of as a potential source of electrophilic hydroxyl, OH+.
Three types of reac
tion are demonstrated:
(a) electrophilic at
tack at an unsubstituted aromatic position, re sulting in the direct introduction of a hydroxyl group, (b) attack at an already substituted ring position, followed by a Wagner-Meerwein re arrangement, leading to either a rearranged phenol or a 2,4-cyclohexadienone, and (c) hy dride abstraction from a methyl group para to a phenolic hydroxyl, leading ultimately to diphenylmethane derivatives.
Finally, the re
agent smoothly converts tetramethylethylene to pinacolone.
All of these reactions proceed
well at — 4 0 ° to 0° C.
ρ or m a n y reasons i t is d e s i r a b l e t o h a v e reagents a v a i l a b l e w h i c h f u n c t i o n as i f t h e y w e r e sources of e l e c t r o p h i l i c o r p o s i t i v e h y d r o x y l , a b b r e v i a t e d i n this p a p e r as O H + . W e r e s u c h reagents a v a i l a b l e , o n e c o u l d e n v i s i o n direct hydroxylation of aromatic compounds,
electrophilic attack o n
d o u b l e b o n d s l e a d i n g to epoxides, to c a r b o n y l c o m p o u n d s , to alcohols, o r e v e n to c a t i o n i c p o l y m e r i z a t i o n i n i t i a t e d b y O H + , g i v i n g l o n g - c h a i n alcohols d i r e c t l y .
T h e present p a p e r describes some oxidations u s i n g
p e r o x y t r i f l u o r o a c e t i c a c i d - b o r o n fluoride as a potent e l e c t r o p h i l i c o x i d a n t ; for c o n v e n i e n c e
o n l y , m e c h a n i s m s w i l l b e w r i t t e n u s i n g O H + as t h e
o x i d a n t a l t h o u g h i t is r e c o g n i z e d t h a t this species is p r o b a b l y n o t t h e true o x i d a n t ( f o r e x a m p l e , t h e p o s i t i v e h y d r o x y l species m a y h a v e t r i f l u o r o acetate o r other l i g a n d s a t t a c h e d ) .
S o m e of t h e reactions a r e c e r t a i n l y 1
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
2
SELECTIVE OXIDATION PROCESSES
u n i q u e a n d afford n e w p r o d u c t s w h i c h o t h e r w i s e w o u l d b e difficult to obtain. O n e c a n imagine that hydrogen peroxide, i n strong acid, m i g h t b e p r o t o n a t e d a n d l e a d to a p o t e n t o x i d a n t .
T h e concentration of protonated
H H—0—0—H
J£
H—Ô—0—H ®
H 0 + 2
p e r o x i d e is e s t i m a t e d to b e a b o u t 1 % i n 10IV a c i d .
0H
(1)
+
T h e hydroxyl cation,
O H + , was the assumed intermediate i n the conversion of mesitylene to mesitol b y hydrogen peroxide i n acetic-sulfuric acid ( 3 ) . boron
fluoride-etherate,
A Lewis acid,
h a s b e e n u s e d i n p l a c e of m i n e r a l a c i d w i t h
h y d r o g e n p e r o x i d e to o x i d i z e m - x y l e n e , i n l o w y i e l d , t o p h e n o l s a n d quinones ( 8 ) . P e r o x y t r i f l u o r o a c e t i c a c i d w a s c o n s i d e r e d to b e a n excellent source o f p o s i t i v e h y d r o x y l because t h e trifluoroacetate i o n is a g o o d l e a v i n g g r o u p
(2).
CF C—O-io-H 3
• CF C0 3
f
2
0H
(2)
+
U s i n g excess p e r a c i d , M u s g r a v e et al. ( 2 ) o b t a i n e d 3 0 - 4 0 % of a l k y l b e n z e n e s to p h e n o l s a n d q u i n o n e s .
conversions
m - X y l e n e g a v e 2,4- a n d 2,6-
x y l e n o l s ; this o r i e n t a t i o n s t r o n g l y suggests t h a t t h e r e a c t i o n hydroxyl cation rather than h y d r o x y l radical.
involves
T h e reaction has been
e x t e n d e d b y M c C l u r e ( 9 ) t o t h e p r e p a r a t i o n of o- a n d p - m e t h o x y p h e n o l s f r o m anisole a n d analogous p h e n o x y p h e n o l s
f r o m d i p h e n y l ether.
The
p r o d u c t s f r o m 2,6-xylenol a n d p e r o x y t r i f l u o r o a c e t i c a c i d d e p e n d
upon
reaction conditions; either 2,6-dimethylbenzoquinone dimethyl-2,4-cyclohexadienone
o r 6-hydroxy-2,6-
d i m e r m a y p r e d o m i n a t e , s l o w a d d i t i o n of
the p e r o x i d e to t h e p h e n o l f a v o r i n g t h e l a t t e r ( 7 ) .
T h e dienone
pre-
s u m a b l y arises b y attack o f O H + at o n e of t h e m e t h y l - s u b s t i t u t e d p o s i tions:
dimer
(3)
M e t h y l migration, v i a a W a g n e r - M e e r w e i n type rearrangement, has also b e e n n o t e d i n a f e w instances ( 2 ) .
F o r e x a m p l e , o x i d a t i o n of 2,4,5-
t r i m e t h y l p h e n o l w i t h p e r o x y t r i f l u o r o a c e t i c a c i d at r o o m t e m p e r a t u r e f o r 24 h o u r s gave some t r i m e t h y l - b e n z o q u i n o n e , p r o b a b l y as s h o w n :
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
I.
HART ET AL.
Peroxytrifluoracetic Acid
OH
OH
3 OH
(4)
A s m a l l y i e l d o f q u i n o l w a s i s o l a t e d , c l e a r l y s h o w i n g attack b y t h e o x i d a n t at t h e s u b s t i t u t e d 4 - p o s i t i o n . A l t h o u g h oxidations w i t h p e r o x y t r i f l u o r o a c e t i c a c i d seems to b e u s e f u l (2, 7, 9 ) , conversions are often l o w a n d t h e use of p e r a c i d is r a t h e r i n efficient.
I t o c c u r r e d to us t h a t a L e w i s a c i d m i g h t f a c i l i t a t e t h e d e c o m -
p o s i t i o n of p e r o x y t r i f l u o r a c e t i c a c i d ( E q u a t i o n 2 ) t h r o u g h c o o r d i n a t i o n w i t h o n e of the oxygens not u s e d u l t i m a t e l y as a n o x i d a n t . A c c o r d i n g l y , t h e reagent, p e r o x y t r i f l u o r o a c e t i c a c i d - b o r o n
fluoride,
a n d s e v e r a l s i m i l a r systems h a v e b e e n i n v e s t i g a t e d as oxidants ( 1 , 5 , J O ) .
Experimental M e s i t o l f r o m M e s i t y l e n e . A m e t h y l e n e c h l o r i d e s o l u t i o n of p e r o x y t r i f l u o r o a c e t i c a c i d w a s p r e p a r e d b y m i x i n g 35 grams (0.167 m o l e ) of trifluoroacetic a n h y d r i d e , 50 m l . of m e t h y l e n e c h l o r i d e , a n d 4 m l . (0.147 m o l e ) of 9 0 % h y d r o g e n p e r o x i d e a t 0 ° C . , t h e n a l l o w i n g t h e s o l u t i o n to w a r m to r o o m t e m p e r a t u r e f o r several m i n u t e s . T h i s p e r a c i d s o l u t i o n , c o o l e d to 0 ° C , w a s a d d e d d r o p w i s e to a s o l u t i o n of 56.1 grams (0.468 m o l e ) of m e s i t y l e n e i n 100 m l . o f m e t h y l e n e c h l o r i d e , d u r i n g w h i c h t i m e b o r o n fluoride (0.147 m o l e ) w a s b u b b l e d t h r o u g h t h e r e a c t i o n m i x t u r e . T h e reaction was strongly exothermic, a n d the temperature was kept b e l o w 7 ° C . b y a salt-ice b a t h ( r e a c t i o n p r o c e e d s w e l l at t e m p e r a t u r e s as l o w as — 4 0 ° C . ) . A f t e r a d d i t i o n w a s c o m p l e t e (2.5 h o u r s ) t h e s o l u t i o n w a s w a r m e d to r o o m t e m p e r a t u r e , h y d r o l y z e d w i t h 100 m l . of w a t e r , a n d w o r k e d u p . W e o b t a i n e d 32.0 grams of r e c o v e r e d m e s i t y l e n e a n d 17.7 grams ( 8 8 % ) o f m e s i t o l , m . p . 6 9 - 7 0 ° C . I n other experiments, r u n at — 4 0 ° C , the y i e l d o f m e s i t o l w a s v i r t u a l l y q u a n t i t a t i v e .
Results and Discussion A d d i t i o n of p e r o x y t r i f l u o r o a c e t i c a c i d to a s o l u t i o n of excess m e s i t y lene i n m e t h y l e n e c h l o r i d e , t h r o u g h w h i c h b o r o n fluoride w a s passed, gave a n e a r l y q u a n t i t a t i v e y i e l d of m e s i t o l , b a s e d o n p e r a c i d u s e d . T h e e x o -
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
SELECTIVE OXIDATION PROCESSES
4
thermic reaction was r u n from —40° to 0° C . w i t h external cooling.
At
h i g h e r temperatures f u r t h e r o x i d a t i o n occurs, a n d t h e y i e l d o f m e s i t o l decreases.
T h e efficiency of t h e process, as m e a s u r e d b y u s e o f p e r a c i d ,
decreases m a r k e d l y i f t h e b o r o n fluoride is o m i t t e d .
T h e r e a c t i o n occurs
as r a p i d l y as p e r a c i d is a d d e d ; w o r k u p f o l l o w s after 15 m i n u t e s s t i r r i n g , f o l l o w i n g c o m p l e t i o n of the a d d i t i o n . I s o d u r e n e is c o n v e r t e d t o i s o d u r e n o l i n 6 5 % y i e l d i n a s i m i l a r m a n n e r . I n the latter case, other p r o d u c t s , as y e t u n i n v e s t i g a t e d , a r e f o r m e d . OH
Extension of t h e reaction to prehnitene l e d to various products ( I I - V I ) i n a d d i t i o n to t h e e x p e c t e d p r e h n i t o l ( I ) . E l u c i d a t i o n o f t h e structures of these p r o d u c t s l e d to s o m e f u r t h e r u n d e r s t a n d i n g of t h e k i n d s of reactions CF3CO3H-BF3 m i g h t i n d u c e a n d to u n i q u e d i e n o n e a n d other syntheses. T h e y i e l d s of I - V I f r o m p r e h n i t e n e a n d C F 3 C O 3 H ,
I
Ε
ΠΙ
IV
V
VI
w i t h a n d w i t h o u t b o r o n fluoride, a r e s u m m a r i z e d i n T a b l e I . I is a c c o u n t e d f o r b y o r d i n a r y e l e c t r o p h i l i c s u b s t i t u t i o n at t h e v a c a n t r i n g p o s i t i o n . I I a n d I I I p r e s u m a b l y arise f r o m e l e c t r o p h i l i c attack at C - l f o l l o w e d b y a m e t h y l shift. I V - V I c a n b e e x p l a i n e d b y h y d r i d e transfer f r o m t h e p a r a - m e t h y l groups o f I a n d I I , f o l l o w e d b y a l k y l a t i o n s a n d d e b e n z y l a t i o n s as s h o w n i n schemes 7 a n d 8. E v i d e n c e that this m e c h a n i s m c a n b e correct i n b r o a d outlines w a s d e r i v e d f r o m a n o x i d a t i o n of c h l o r o m e s i t y l e n e . Chloromesitylene was o x i d i z e d at 5 ° - 7 ° C . w i t h p e r o x y t r i f l u o r o a c e t i c a c i d a n d b o r o n fluoride i n m e t h y l e n e c h l o r i d e , u s i n g 2.4 m o l e s o f substrate p e r m o l e of o x i d a n t . T h e o x i d a t i o n w a s r e a s o n a b l y efficient, 0.85 m o l e s of c h l o r o m e s i t y l e n e b e i n g c o n s u m e d p e r m o l e of p e r a c i d . T h r e e c r y s t a l l i n e p r o d u c t s w e r e i s o l a t e d ; the m a j o r one, f o r m e d i n at least 3 9 % y i e l d , m e l t e d at 142.5-143.5° C . A d e t a i l e d s t u d y o f its N M R a n d mass s p e c t r u m suggested that i t w a s V I I I .
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
I.
HART ET AL.
Peroxytrifluoracefic
5
,C1
,C1
H0-
Acid
Ή· 2
ΙΛ
HO
" ^ [ ^
VIII
Table I.
C
H
2
" ^ ^ ~
IX
Summary of Oxidation of Prehnitene with C F C 0 H 3
With BFz Prehnitene used (mmoles) P e r a c i d used (mmoles) Prehnitene recovered (mmoles) Efficiency (prehnitene o x i d i z e d / p e r a c i d used),
Products
%
%of Prehnitene Oxidized 9.1 3.6 1.8
3.0 1.2 0.58
—
Total R e s i d u e (grams)
—
Moles
%of Prehnitene Oxidized
2.2 2.0 1.1 2.0
19.0 17.2 9.5 17.2 7.8
4.8 1.8
14.5 5.4
0.9
3.9
23.6
(small)
15.3
58.0
8.2
1.2
a This compound is tentatively assigned the structure hexadienone.
BFz
121.0 38.3 109.4 30.3
121.0 38.3 87.9 86.2
Moles
P r e h n i t o l (I) Isodurenol ( I I ) Gyclohexadienone (III) U n k n o w n , mass 1 8 2 ° 2,3,5-Trimethylphenol ( I V ) 2,3,6-Trimethylphenol ( V ) 2,2 ',3,3 ',4,4 ',5,5 ' - O c t a m e t h y l d i p h e n y l methane ( V I )
3
Without
70.7 0.8
2,4-dihydroxy-3,4,5,6-tetramethyl-2,4-cyclo-
OH"*
(7)
*CH
OH
1
CH
HO
8
II
+
III
(8)
2
VII /A similar scheme, \starting w i t h I I , accounts for V )
Η VI
Prehnitene, +
C
H
2
^
^
+
IV
—H ( W +
^-CH —V 2
\
P o s t u l a t e d M e c h a n i s m s f o r O x i d a t i o n of P r e h n i t e n e
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
SELECTIVE OXIDATION PROCESSES
6
T h e structure w a s confirmed b y reduction w i t h l i t h i u m sand to I X , m.p. 121°-123° C , a n authentic sample of w h i c h was synthesized from chlorom e t h y l m e s i t y l e n e a n d 2,6-xylenol. i n structure to c o m p o u n d
It w i l l b e noted that V I I I
V I I i n the proposed
corresponds
oxidation scheme for
prehnitene. T h e other t w o o x i d a t i o n p r o d u c t s o f c h l o r o m e s i t y l e n e w e r e i s o l a t e d pure i n approximately 1 0 % y i e l d each.
O n e of these, m . p . 8 3 ° - 8 4 ° C ,
was i d e n t i c a l ( I R , N M R ) w i t h a s a m p l e of 3 - c h l o r o m e s i t o l ( X ) p r e p a r e d b y c a r e f u l c h l o r i n a t i o n of m e s i t o l . 118°-119
0
T h e other, w h i t e p r i s m s m e l t i n g a t
C , is assigned s t r u c t u r e X I o n t h e basis o f e l e m e n t a l analysis
a n d N M R s p e c t r u m ( s h a r p singlets at 7.96, 7.85, 7.75, 5.97, a n d 3.21 w i t h r e l a t i v e areas 3 : 3 : 3 : 1 : 1 ) . CH3.i
H
CH
C o m p o u n d X I corresponds t o c o m p o u n d V I
3
C
£ y
c
l
CH -/^-CH -/~V-CH 3
2
CH
CH
3
3
3
XI i n the prehnitene
oxidation.
D e b e n z y l a t i o n is less i m p o r t a n t i n t h e
c h l o r o m e s i t y l e n e o x i d a t i o n t h a n i n t h e p r e h n i t e n e o x i d a t i o n (—i.e., V I I I is less r e a d i l y d e b e n z y l a t e d t h a n V I I ) p r o b a b l y b e c a u s e o f t h e d e s t a b i l i z i n g influence of the c h l o r o s u b s t i t u e n t o n the i n t e r m e d i a t e b e n z y l c a t i o n . N i t r o m e s i t y l e n e , o x i d i z e d u s i n g a n excess o f a r o m a t i c , g a v e o n l y a single crystalline product, m.p. 244°-245° C , i n 2 1 % y i e l d .
T h e product
is a s s i g n e d s t r u c t u r e X I I b a s e d o n a n a l y s i s , i n f r a r e d a n d N M R s p e c t r a , and analogy w i t h V I I I .
T h e l o w recovery of pure, unreacted nitromesity-
lene ( o n l y a b o u t 6 0 % of t h e o r y ) a n d f o r m a t i o n of c o n s i d e r a b l e a m o u n t s of i n t r a c t a b l e t a r suggest that t h e s t r o n g l y e l e c t r o n - w i t h d r a w i n g n i t r o g r o u p i n h i b i t s t h e n o r m a l e l e c t r o p h i l i c s u b s t i t u t i o n b y O H + a n d favors
side
reactions. N0
2
CH
3
N0 C H 2
3
-OH
A t t h i s p o i n t t h e n , o n e c a n s u m m a r i z e that three types o f reactions h a v e b e e n d e m o n s t r a t e d f o r the reagent C F C 0 H - B F : 3
3
3
(a) E l e c t r o p h i l i c a t t a c k a t a n u n s u b s t i t u t e d a r o m a t i c p o s i t i o n r e s u l t ing i n the direct introduction of a h y d r o x y l group. ( b ) A t t a c k at a l r e a d y s u b s t i t u t e d r i n g p o s i t i o n , f o l l o w e d b y a W a g n e r - M e e r w e i n rearrangement, l e a d i n g to either a rearranged phenol or a 2,4-cyclohexadienone.
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
I.
HART ET AL.
7
Peroxytrifiuoracetic Acid
(c) H y d r i d e abstraction from a m e t h y l group p a r a to a h y d r o x y l g r o u p , l e a d i n g u l t i m a t e l y to d i p h e n y l m e t h a n e d e r i v a t i v e s . It seemed further.
p a r t i c u l a r l y d e s i r a b l e to e x p l o i t t h e d i e n o n e
synthesis
E m b o l d e n e d b y the recovery of cyclohexadienone I I I from the
o x i d a t i o n of p r e h n i t e n e , a l b e i t i n l o w y i e l d , w e a p p l i e d t h e r e a g e n t t o hexamethylbenzene h o p i n g that dienone w o u l d b e the major
product.
T h e s e efforts w e r e r e w a r d e d since t h e o x i d a t i o n o f h e x a m e t h y l b e n z e n e w i t h C F 3 C O 3 H - B F 3 at 0 ° C . g a v e the c r y s t a l l i n e d i e n o n e X I I I ( m . p . a b o u t room temperature) i n over 9 0 % yield.
T h e structure of X I I I was demon-
CF CQ H-BF 3
3
3
(9)
0°C., >90% XIII
strated b y its e l e m e n t a l a n a l y s i s , spectra, a n d c h e m i c a l conversions, some of w h i c h are s h o w n i n S c h e m e 10. HQ LiAlH ^ 4
Ύ
H y~
-
H
^
+
a
]
i
t
t
l
e
(10)
azodicarboxylate
/ / ι , > > ^ / ^ N
^C0 Et 2
H e x a e t h y l b e n z e n e i s s i m i l a r l y o x i d i z e d i n h i g h y i e l d to h e x a e t h y l - 2 , 4 cyclohexadienone.
S u r p r i s i n g l y , the m a j o r p r o d u c t s f r o m the o x i d a t i o n of
p e n t a m e t h y l b e n z e n e a r e dienones, n o p e n t a m e t h y l p h e n o l b e i n g d e t e c t e d b y gas c h r o m a t o g r a p h y . BF
3
E v e n the oxidation of durene w i t h CH3CO3H-
g a v e over 5 0 % y i e l d of d i e n o n e X I V a n d v e r y l i t t l e d u r o q u i n o n e ( 6 ) . CF CQ H-BF ^ 3
3
3
f^f°
>S
XIV
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
(11)
SELECTIVE OXIDATION PROCESSES
8
F i n a l l y , the intermediate envisioned w h e n one adds O H + to a tetra s u b s t i t u t e d olefin resembles c l o s e l y the i n t e r m e d i a t e c a t i o n i n t h e p i n a c o l pinacolone rearrangement.
I t s e e m e d d e s i r a b l e , therefore, t o c a r r y o u t
an oxidation of tetramethylethylene w i t h CF3CO3H-BF3.
W h e n this w a s
d o n e , a t — 4 0 ° C . i n m e t h y l e n e c h l o r i d e as solvent, a n e a r l y q u a n t i t a t i v e v i e l d of pinacolone was obtained. GH,
/
CF|CO«H—BF, > GH —G—G(CH )Î 3
3
-40° to 0°C.
Î-H,
(12)
-G—C(CH ) 8
C H s ^ ^ O H ^ H a
8
ÔH
W h e n B F w a s o m i t t e d , the y i e l d o f p i n a c o l o n e w a s r e d u c e d t o 1 6 % , a n d 3
the m a j o r p r o d u c t w a s t h e h y d r o x y - t r i f l u o r o a c e t a t e X V w h i c h o n t r e a t m e n t w i t h b o r o n fluoride g a v e p i n a c o l o n e q u a n t i t a t i v e l y . GH
C H
3
\ CH
A
G
8
O H
Ο
3
II
BF,
/ G l \ IG H O — G GFj
>
GH —G—C(GHt)i 3
(13)
3
A
X V
F r o m these results, i t i s c l e a r t h a t p e r o x y t r i f l u o r o a c e t i c fluoride
acid-boron
is a n e x t r e m e l y p o t e n t o x i d a n t c a p a b l e o f v a r i o u s h i g h l y selective,
u n i q u e , a n d u s e f u l o x i d a t i o n s , a n d its use i n synthesis i s b e i n g i n v e s t i g a t e d further.
T h e e x p e r i m e n t a l details o f these o x i d a t i o n s w i l l b e p r e s e n t e d
e l s e w h e r e , b u t a t y p i c a l o x i d a t i o n o f m e s i t y l e n e to m e s i t o l i s g i v e n h e r e t o i l l u s t r a t e the g e n e r a l p r o c e d u r e u s e d .
Acknowledgment We
are i n d e b t e d to t h e d o n o r s o f t h e P e t r o l e u m R e s e a r c h
administered b y the A m e r i c a n C h e m i c a l Society
(G-488C)
Fund
a n d to the
N a t i o n a l S c i e n c e F o u n d a t i o n ( G P - 7 1 ) f o r financial s u p p o r t .
Literature Cited (1) Buehler, C . Α., H a r t , H . , J. Am. Chem. Soc. 85, 2177 ( 1 9 6 3 ) . (2) Chambers, R . D . , G o g g i n , P . , Musgrave, W . K . R . , J. Chem. Soc. 1959, 1804. (3) Derbyshire, D . H., Waters, W. Α., Nature 1 6 5 , 4 0 1 (1950). (4) D o e r i n g , W . , v o n E. Saunders, M., Boyton, H. G., Earhart, H . W., W a d l e y , E . F . , E d w a r d s , W . R., L a b e r , G., Tetrahedron 4 , 1 7 8 ( 1 9 5 8 ) .
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
1.
HART ET AL.
Peroxytrifluoracetic Acid
(5) Hart, H., Buehler, C. Α., J. Org. Chem. 29, 2397 (1964). (6) Hart, H . , Lange, R., unpublished results. (7) McClure, J. D., J. Org. Chem. 28, 69 (1963). (8) McClure, J. D., Williams, P. H., Ibid. 27, 24 (1962). (9) McClure, J. D., William, P. H., Ibid. 27, 627 (1962). (10) Waring, A. J., Hart, H . , J. Am. Chem. Soc. 86, 1454 (1964). RECEIVED November 13, 1964.
Fields; Selective Oxidation Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1965.
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