Synthesis of Substituted Cyclopentadienones by Ring Contraction.

The structures of the esters (5a) and (56) were proved by
elemental analyses, by IR, 1H-NMR, and mass spectra, and
also chemically, by decarbonylation of the dimethyl acetylenedicarboxylate Diels-Alder adduct 131 of (5a) to give triBy W . Ried, W . Kunkel, and P . B. OIschewski[*l
methyl 6'-benzyl-p-terphenyl-2',3',5'-tricarboxylate and by
In attempts to convert 5-alkoxy-3-benzyl-5-hydroxy-2,6-di- reductionr4J of (5a) with zinc and glacial acetic acid to
methyl 5 - benzyl- 3 - oxo-2,4-diphenyl-2-cyclopentenecarboxphenyl-2-cyclohexene-1,4-diones(3a) and (36) by a n excess
ylate.
of acetic anhydride into the acetyl compounds ( 4 a ) and ( 4 b )
Received: January 2, 1969; revised: January 24, 1969 [ Z 945 IE]
and thence by loss of acetic acid into the alkoxy quinones
German version: Angew. Chem. 81, 260 (1969)
(612)and ( 6 b ) 111, respectively, gave, not only the expectedcompound ( l a ) or ( 4 6 ) . but also surprisingly the new, deep
-car[*] Prof. Dr. W. Ried, Dr. W. Kunkel, and P. B. Olschewski
red 5-benzyl-3-oxo-2,4-diphenyl-l.4-cyclopentadiene-l
Institut fur Organische Chemie der Universitat
boxylates (5a) [m.p. 158 OC (from methanol); I R spectrum,
6 Frankfurt, Robert-Mayer-Strasse 7-9 (Germany)
vco = 1720 cm-1; IH-NMR spectrum (in CDC13) [21, T =
2.5-3.0 (15 H), D; T = 5.9 (2 H), S; 7 = 6.65 (3 H), S ] and
[l] W. Ried and W. Kunkel, Liebigs Ann. Chem. 717, 54 (1968).
( 5 b ) [m.p. 105 "C (from methanol or ethanol); I R spectrum,
[2] The IR spectra were measured o n a Perkin-Elmer grating
vco = 1720cm-I]. Compound (30) or (36) (2.5mmoles)
spectrometer 337 and the NMR spectra on a Varian A-60 inwas heated with acetic anhydride (60 ml), the initial colorless
strument with tetramethylsilane as internal standard.
solution becoming deep red; the hot mixture was poured into
[3] M . A . Ogliaruso, M . G . Romanelli, and E. I. Becker, Chem.
water.
Reviews 65, 261 (1965).
n
[4] D . A . Brown, J . P. Hargaden, C . M . McMullin, N . Gogan, and
H. Sloan, J. chem. SOC.(London) 1963, 4914; N . 0. V . Sonntag,
c6H5fJc6H5
S. Linder, E. I. Becker, and P. E. Spoerri, J . Amer. chem. SOC.75,
2283 (1953).
R
OH
Synthesis of Substituted Cyclopentadienones by
Ring Contraction
0
J.
Alkali-Metal Tetraorganylboratesfrom
Triorganyl boranes
By M. A . Grassberger and R . Koster[*J
Tetraorganylborates are of importance for the preparation
of organic and organometallic compounds and as analytical
reagents
We have found that the alkali-metal tetraorganylborates ( 2 ) - ( 9 ) can be prepared from alkali-metal tetraethylborates (1) and triorganylboranes at 130-180 "C in accordance with reaction (a) (cf. Table 1). Presence of solvent
is not usually necessary.
3 MB(CzH5)4 + 4 BR3
(la), M
(lb), M
=
=
+
Li
Na
3 MBR4
+ 4 B(CzH5)3
(a)
(2i-(91
f6)
'6"5fJCCH5
OR'
R
0
The mixed products were separated by chromatography o n
silica gel with benzene as eluant. The yields of (5n) and (56)
increased monotonically with increasing reaction time. After
6-hours' heating of (3a) or (36) in acetic anhydride the
yields obtained were 10% of ( 5 a ) with 64% of ( 4 0 ) [m.p.
168°C (from light petroleum); vco = 1710, 1740cm-l] or
16.5 % of ( 5 b ) with 61 % of ( 4 6 ) [m.p. 127 "C (from light
petroleum); vco = 1710, 1730 cm-11.
The acetyl compounds (4a) and ( 4 6 ) can also be converted
into the esters (5a) and (561, respectively, and are thus
apparently intermediates. However, it is unlikely that the
alkoxy quinones ( 6 ) are intermediates in production of the
five-membered ring compounds as the known compound
(6a) [I] is not converted into ( 5 a j under the above reaction
conditions.
For synthesis of the starting materials (3a) [m.p. 136OC
(from methanol or light petroleum; vco = 1730 cm-11 and
(36) [m.p. 15OoC (from ethanol or light petroleum);
vco = 1720,1740 cm-~],3-benzyl-5-hydroxy-2,6-diphenyl-l.4benzoquinone ( l a ) was converted into ( 2 a ) [m.p. 149 O C
(from methanol); vco = 1740, 1750cm-11 and (2bj [m.p.
127 OC (from ethanol); vco = 1740, 1750 cm-11, respectively,
by bromine or N-bromosuccinimide in the presence of methanol or ethanol, respectively, and then debrominated catalytically by hydrogen o r by treatment with zinc in glacial
acetic acid.
Angew. Chem. internat. Edit. 1 VoI. 8 (1969)
1 No. 4
Table 1.
Alkali-metal tetraorganylborates MBR4.
M
R
Temp.
Yield
( "C)
( %)
140
130
140
135
140
180
160
140
145
100
Na
Na
Na
Na
Na
Li
Li
Na
Na
Butyloxy
Allyloxy
Crotyl
Methallyl
Ial
Phenyl
Benzyl
Benzyl
Pyrrolyl
77
S6
85
91
92 b
70
95
81
l
>350
> 350
130
166
30
>350
198
200
> 350
[a] cis-trans mixture of isomers. See eq. (c) for formula.
[b] Obtained with a 50% excess of BR,.
[c] All compounds except (66) decompose on melting.
In solution, a n equilibrium always sets in. For example, compound (5b1 reacts with an equimolar amount of triethylborane in dimethyl sulfoxide at room temperature to give
trimethallylborane and sodium triethylmethallylborate.
The hitherto unreported sodium tetraallylborates ( 4 6 ) and
(5b), as well as sodium tetrabenzylborate (86), can, in
particular, be obtained in good yields from the easily accessible [21 sodium tetraethylborate (16) (m.p. 144 "C).The alkalimetal tetraethylborate can be recovered by reaction of alkalimetal hydride and ethylene with the triethylborane formed at
the same time in reaction (a) 121.
275