J. Am. Chem. Soc. 1998, 120, 4015-4016
4015
Communications to the Editor
Scheme 2
New Type of Photochemical Carbon Skeletal
Rearrangement: Transformation of r,â-Unsaturated
Carbonyl to 1,4-Dicarbonyl Compounds
Shoji Matsumoto, Yasutaka Okubo, and Koichi Mikami*
Department of Chemical Technology
Tokyo Institute of Technology
Meguro-ku, Tokyo 152, Japan
ReceiVed July 16, 1997
Reactions of carbonyl compounds in photoexcited states have
attracted much attention, and hence, the precedented examples
are well classified.1 However, we herein report a new type of
photochemical carbon skeletal rearrangement of R-hydroxym-
ethylated R,â-unsaturated carbonyl compounds (1). Molecules
of type 1 selectively rearrange to 1,4-dicarbonyl compounds 2,
which are highly desirable intermediates for the synthesis of
cyclopentenones and five-membered heterocycles2 (Scheme 1).
The substrates 1 were easily prepared by the Baylis-Hillman
reaction of R,â-unsaturated carbonyl compounds with aldehydes.3,4
Therefore, the overall transformation can be regarded as 1,4-
addition of acyl anions derived from the aldehydes to the starting
R,â-unsaturated carbonyl compounds.5 This new and synthetically
interesting pathway to 1,4-dicarbonyl compounds is the subject
of this paper.
Table 1. Rearrangement of R,â-Unsaturated Carbonyl Compounds
1a
substrate 1
R1
R2
2 (% yield)
a
b
c
d
e
f
Me
Ph
53
p-MeO-Ph
p-Cl-Ph
Ph
41
66
Ph
54
Me
Et
62b
50c
a Irradiated for 6 h in 0.01 M benzene solution with high-pressure
mercury lamp. b Irradiated for 4 h. c Irradiated for 2 h.
Scheme 1
The enones 1 was irradiated with a high-pressure mercury lamp,
and the 1,4-dicarbonyl compounds 2 were isolated simply by silica
gel chromatography through carbon skeletal rearrangement with
almost complete consumption of 1 (<8% recovery).6 The present
carbon skeletal rearrangement can be applied to a variety of alkyl-
and aryl-substituted ones (1) (Table 1). The quantum yields with
1a or 1e at 313 nm using valerophenone as an actinometer7 were
calculated to be ca. 0.1. This rearrangement can be quenched
by a triplet quencher, NaI.8 The substrates without hydroxy group
at the allylic position such as 2-methyl-1-phenyl-2-penten-1-one
did not give any rearrangement product 2 under the same reaction
conditions. This suggests the requirement for the hydroxy group
to weaken the allylic C-H bond.
(1) (a) Special issue on photochemical strategy in organic synthesis:
Ramamurthy, V., Turro, N. J., Eds. Chem. ReV. 1993, 93 (1). (b) Mattay, J.;
Griesbeck, A. G. Photochemical Key Steps in Organic Synthesis; VCH: New
York, 1994. (c) Yoon, U. C.; Mariano, P. S. Acc. Chem. Res. 1992, 25, 233.
(d) Gilbert, A.; Baggott, J. Essentials of Molecular Photochemistry; Blackwell
Scientific: Oxford, 1991. (e) Wagner, P. J.; Park, B.-S. Org. Photochem. 1991,
11, 227. (f) Porco, J. A., Jr.; Schreiber, S. L. ComprehensiVe Organic Synthesis;
Pergamon: London, 1991; Vol. 5, p 151. (g) Demuth, M.; Mikhail, G.
Synthesis 1989, 145. (h) Crimmins, M. T. Chem. ReV. 1988, 88, 1453. (i)
Rearrangements in Ground and Excited States; de Mayo, P., Ed.; Academic
Press: New York, 1980; Vol. 3. (j) Koizumi, M.; Kato, S.; Mataga, N.;
Matsuura, T.; Usui, Y. Photosensitized Reactions; Kagakudojin: Kyoto, 1978.
(2) (a) Texier-Boullet, F.; Klein, B.; Hamelin, J. Synthesis 1986, 409. (b)
Trost, B. M. Chem. Soc. ReV. 1982, 11, 141.
To clarify the intra- or intermolecular courses, the crossover
experiment was examined between 1c and 1f (Scheme 2).
However, bimolecular products (2c′ or 2f ′) were not observed
at all, thus indicating that this reaction proceeds in an intramo-
lecular fashion.
To gain a deeper insight into the mechanism, we next examined
the methyl- and silyl-protected substrates 3c and 5a, respectively
(3) (a) Basavaiah, D.; Rao, P. D.; Hyma, R. S. Tetrahedron 1996, 52, 8001.
(b) Drewes, S. E.; Roos, G. H. P. Tetrahedron 1988, 44, 4653.
(Scheme 3). After irradiation of 3c for 6 h, the rearrangement
product 4c9 and the resultant 1,4-dicarbonyl compound 2c were
isolated by silica gel chromatography in 68% combined yield.
(4) Procedure for the Baylis-Hillman reaction as follows: To a solution
of R,â-unsaturated carbonyl compound (methyl vinyl ketone or phenyl vinyl
ketone) and aldehyde (1-2 equiv) in THF was added DABCO (15 mol %)
and stirred for 7-10 days at room temperature. The reaction mixture was
poured into saturated NH4Cl solution. Standard workup followed by silica-
gel chromatography afforded the product (1) in 15-86% yield.
(5) For reviews on the synthesis of 1,4-dicarbonyl compounds, see: (a)
Stetter, H.; Kuhlmann, H. Org. React. 1991, 40, 407. (b) Miyakoshi, T. Org.
Prep. Proc. Int. 1989, 21, 659. (c) Reissig, H.-U. Top. Curr. Chem. 1986,
144, 73. (d) Via 1,4-addition reaction of radicals: Vassen, R.; Runsink, J.;
Scharf, H.-D. Chem. Ber. 1986, 119, 3492 and references therein.
(6) When 1d, 1e and 1f were used, 1,3-dicarbonyl compounds were obtained
in about 10-26% yields by olefin isomerization. No other byproduct was
1
observed in the crude H NMR spectra.
(7) Lewis, F. D.; Hilliard, T. A. J. Am. Chem. Soc. 1972, 94, 3852.
(8) Fukuzumi, S.; Kuroda, S.; Tanaka, T. J. Am. Chem. Soc. 1987, 109,
305.
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Published on Web 04/14/1998
Matsumoto
