J. Org. Chem. 1990,55, 2443-2445
2443
Regiocontrolled Cyclohexenone Annulation via Acylation of a Ketone Carbonyl Leo A. Paquette,* Choon Sup Ra, and Scott D. Edmonson’ Evans Chemical Laboratories, The Ohio State University, Columbus, Ohio 43210 Received November 17, 1989
1-(1-Ethoxyvinyl)cycloalkenes,readily available by palladium-catalyzed condensation of enol triflates with ethyl vinyl ether or its a-trimethylstannyl derivative, enter into Diels-Alder reaction with (2)-1,2-bis(phenylsulfony1)ethylene. These adducts undergo smooth reductive desulfonylation to provide cyclohexenones after enol ether hydrolysis. Migration of the double bond into the thermodynamically more stable internal conjugated position completes the annulation scheme.
While developing a synthetic entry to a complex natural product, we had need for effecting the following conversion smoothly under mild conditions. This transformation has been accorded surprisingly little a t t e n t i ~ n . ~ In - ~ fact, the only effective pathway known to us is a seven-step transformation developed by House.6 However, this process includes steps that precluded its use for our purpose.’
Scheme I &OEt
1
0
As a potentially serviceable alternative strategy, we envisioned milder indirect acylation of the carbonyl group so as to allow for six-membered ring construction via subsequent [4 21 cycloaddition. Introduction of the desired double bond would then be implemented via controlled reductive elimination conditions? We focused on 3-ethoxybutadienes such as 3 (Scheme I) because of the ready availability of ethyl vinyl ether and its a-trimethylstannyl derivative:JO and the striking ease with which these reagents can be coupled to vinyl triflates.11J2 The advantages offered by the new protocol were considered to be the chemospecific and regiospecific C-C coupling exemplified by 2 3, the activation inherent in
+
-
(1) Undergraduate Research Participant, Summer 1989. (2) The reader will recognize that the desired overall chemical change is the equivalent of a homo-Nazarov sequence although the sequences are totally unrelated mechanistically. For recent work in the Nazarov area, see refs 3-5. (3) Paquette, L. A.; Fristad, W. E.; Dime, D. S.; Bailey, T. R. J . Org. Chem. 1980, 45, 3017 and references cited therein. (4) (a) Santelli-Rouvier, C.; Santelli, M. Synthesis 1983, 429. (b) Ramaiah, M. Ibid. 1984, 529. (c) Ono, M. J. Syn. Org. Chem. Jpn. 1981, 39, 872. (5) Denmark, S. E. Comprehensive Organic Synthesis, Vol. 5; Pergamon Press. in Dress. (6) House, H. 0.;Giese, R. W.; Kronberger, K.; Kaplan, J. P.; Simeone, J. F. J . Am. Chem. SOC.1970, 92, 2800. (7) A reaction scheme that might be adaptable to this purpose has been developed by Chan, T.H.; Prasad, C. V. C. J. Org. Chem. 1987,52, 110. (8) Trost, B. M.; Arndt, H. C.; Strege, P. W.; Verhoeven, T. R. Tetrahedron Lett. 1976, 3477. (9) Cheney, D. L.; Paquette, L. A. J . Org. Chem. 1989, 54, 3334. (10) Analogous chemistry has previously been effected with (a-alkoxyviny1)zinc chlorides [Negishi, E.; Luo, F.-T. J . Org. Chem. 1983, 48, 15601, (a-ethoxyviny1)tributylstannane[Kosugi, M.; Sumiya, T.; Obara, Y . ;Suzuki, M.; Sano, H.; Migita, T. Bull. Chem. SOC. Jpn. 1987,60, 7671, and (a-ethoxyviny1)trimethylsilane[Hatanaka, Y.; Hiyama, T. J . Org. Chem. 1988, 53, 9181. (11) (a) Scott, W. J.;Crisp, G. T.;Stille, J. K. J . Am. Chem. Soc. 1984, 106, 4620. (b) Scott, W. J.; Stille, J. K. Ibid. 1986 108, 3033. (12) Anderson, C.-M.; Hallberg, A. J . Org. Chem. 1989, 54, 1502.
dienes such as 3 for facilitating cycloaddition to the acetylene equivalent (Z)-l,2-bis(phenyls~lfonyl)ethylene,~~ the lack of concern for stereochemistry during the conversion of 3 into 5 , and the reliability offered by Rh(II1) salts for isomerizing the unsaturated linkage into the thermodynamically favored location central to the two rings.14 Direct arrival a t 3 was possible by two methods. The first involved carbon-carbon bond formation by means of (a-ethoxyviny1)stannane a n d tetrakis(tripheny1pho~phine)palladium.~ The alternative use of ethyl vinyl ether and palladium acetate as co-reagents12 proved somewhat more simple and expedient, although the yield of product in both instances was notably high (97%). A lesser amount of noble metal catalyst is required (3 mol % Pd(OAcI2 vs 5 mol % Pd(PPh,),). Also, the product (13) (a) De Lucchi, I.; Lucchini, V.; Pasquato, L.; Modena, G. J . Org. Chem. 1984,49, 596. (b) Paquette, L. A.; Kunzer, H.; Green, K. E.; De Lucchi, 0.;Licini, G.; Pasquato, L.; Valle, G. J. Am. Chem. SOC.1986,108, 3453. (c) De Lucchi, 0.; Modena, G. Tetrahedron 1984,40, 2585. (14) (a) Grieco, P. A.; Nishizawa, M.; Marinovic, N.; Ehmann, W. J. J . Am. Chem. SOC. 1976, 98, 7102. (b) Andrieaux, J.; Barton, D. H. R.; Patin, H. J . Chem. Soc., Perkin Trans. I 1977, 359.
0022-3263/90/ 1955-2443$02.50/0 0 1990 American Chemical Society
2444 J . Org. Chem., 1/01, 55,
Paquette et al.
8 , 1990
Scheme I1 OEt
OTf
W
