Functionalisedcis-Alkenes from the Stereoselective Decomposition of Diazo Compounds, Catalysed by [RuCl(η5-C5H5)(PPh3)2

Abstract

A catalytic amount of [RuCl(η5-C5H5)(PPh3)2] (1) (0.1 mol-%) at 60 °C stereoselectively decomposes α-diazo carbonyl compounds N2CHCOR [R = EtO, Me, Et, nPr, iPr, Ph, (CH2)10Me, and (CH2)14Me] affording quantitatively RCOCH=CHCOR carbene dimers [R = EtO (10), Me (11), Et (12), nPr (13), iPr (14), Ph (15), (CH2)10Me (16), and (CH2)14Me (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-R1COCH=CHCOR2 (18−32), and symmetrical cis-R1COCH=CHCOR1 and cis-R2COCH=CHCOR2 alkenes. The unsymmetrical cis-alkenes 23−32 are formed in about 50% yield from the reaction between two α-diazo ketones. The yield of the cis-R1COCH=CHCOR2 compounds 18−22 increases to ca. 60% when a mixture of α-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 α,ω-bis(diazo) ketones N2CHCO(CH2)nCOCHN2 (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.