Functionalised cis-Alkenes from the Stereoselective Decomposition of Diazo Compounds, Catalysed by [RuCl(eta(5)-C5H5)(PPh3)2]

A catalytic amount of [RuCl(eta(5)-C5H5) (PPh3)(2)] (1) (0.1. mol-%) at 60 degrees C stereoselectively decomposes cr-diazo carbonyl compounds N2CHCOR [R = EtO, Me, Et, nPr, iPr, Ph, (CH2)(10)Me, and (CH2)(14)Me] affording quantitatively RCOCH=CHCOR carbene dimers [R = EtO (10), Me (11), Et (12), nPr (13), iPr (14), Ph (15), (CH2)(10)Me (16), and (CH2)(14)Me (17)]. The cis isomer is formed in 95-99% purity. depending on the R group. Under the same experimental conditions, N2CHCOR1 and N2CHCOR2 react in equimolar amounts to give mixtures of unsymmetrical cis-(RCOCH)-C-1=CHCOR2 (18-32), and symmetrical cis-(RCOCH)-C-1=CHCOR1 and cis-(RCOCH)-C-2=CHCOR2 alkenes. The unsymmetrical cis-alkenes 23-32 are formed in about 50% yield from the reaction between two alpha-diazo ketones. The yield of the cis-(RCOCH)-C-1=CHCOR2 compounds 18-22 increases to ca. 60% when a mixture of alpha-diazo ketone and N2CHCOOEt is catalytically decomposed. Higher conversions into the unsymmetrical products have been obtained by treating N2CHCOR and N2CHSiMe3, from which cis-RCOCH=CHSiMe3 derivatives 34-41 are formed in 83-91% yield. The catalytic decomposition of alpha,omega-bis(diazo) ketones N2CHCO(CH2)(n)COCHN2 (n = 4, 8, or 10) has also been investigated, and found to afford cyclic cis-alkenes arising from both intra- [n = 4 (45), 8 (46), and 10 (47)] and intermolecular carbene-carbene coupling processes.