J. Org. Chem. 1985,50, 3945-3946 A new lactone synthesis15proved effective for the conversion of diiodide 4c to bakkenolide A-viz., the methyl acrylate derivative 5 in DME a t -58 "C on successive treatment with 1.0 equiv of lithium bis(trimethylsily1)amide in DME, 0.9 equiv of the diiodide in HMPA, and then once again with 1.0 equiv of the amide base furnished directly in 69% yield hydrindane 6 as a ca. 3:l mixture (NMR) of C-7 epimers.16 Deprotection-lactonization of 6 occurred on brief contact with aqueous hydrofluoric acid in acetonitrile" to produce in essentially quantitative yield the corresponding spiro @-methylene-y-butyrolactones, from which pure racemic bakkenolide A (1),lomp 47-48 "C, was readily obtained by crystallization from cold pentane. This material was indistinguishable spectroscopically (IR,NMR, MS) and chromatographically (TLC, VPC) from an authentic sample of the natural product. Work directed a t extending this efficient approach to the synthesis of other bakkanes is planned. Acknowledgment. We thank Professor A. Rassat and Dr. J.-L. Luche for their interest in this work and Professor T. Kat0 for a sample of natural bakkenolide A. Financial support from the C.N.R.S. (LA 332) and a fellowship award from the C.N.Pq. (to F.C.) are gratefully acknowledged. (15) Greene, A. E.; Coelho, F.; Deprgs, J.-P.; Brocksom, T. J. J . Org. Chem. 1985,50, 1973-1975. (16) This favorable selectivity, although somewhat less than had been hoped for, was expected on the assumption that the ester dienolate would preferentially react through a 'U-shape" and in such a way as to avoid bringing the bulky -CH20Si(CH3)2(C4Hg) group and the C-5 methyl group into proximity. See: Cainelli, G.; Cardillo, G.; Contento, M.; Trapani, G.; Umani Ronchi, A. J.Chem. SOC., Perkin Trans. 1 1973,400-404, and references cited therein. The use of sodium bis(trimethylsily1)amidein place of the lithium amide, THF in lieu of DME, or smaller amounts of HMPA (70
