A stereospecific rhodium catalyzed hydroacylation. Cyclization of trans-4-hexenal-1-d

Treatment of trans-4-hexenal-1-d with RhCl(PPh3)3 (I) in C6 H6 afforded 2-methylcyclopentanone-3-d and -2-d (II-3-d, and II-2-d) in 91 ratio when the reaction was carried to a low conversion. The deuterium in the II-3-d product was found to be cis to the C(2) methyl group by analysis of the 270 MHz 1H and 41.4 MHz 2H NMR spectra. This analysis was assisted by the synthesis of II-cis-2,3-d2 by treatment of 2-methylcyclopent-2-en-1-one with D2 and I. The 270 MHz 1H and 41.4 MHz 2H spectra of II-cis-2,3-d2 and of II-2,5,5-d3 were instrumental in the assignments of proton resonances in spectra of II-3-d. The results demonstrated that the cyclization of 4-hexenal-1-d occurred by a syn addition of the CD bond to the olefinic bond to generate II-3-d. The results were interpreted in terms of a mechanism involving intervention of an acylrhodium(III) hydride complex and organorhodium(III) intermediates derived therefrom.