Facial diastereoselectivity in cationic propargylations with planar-chiral areneCr(CO)3-substituted propargyl cations

The planar-chiral (o-methoxyphenyl) chromium tricarbonyl-substituted propargyl cation 4 reacts with silyl enol ether derivatives 5 with poor and with enamines 6 with good facial diastereoselectivity to give rise to the (arene)carbonylchromium-substituted propargylated cyclohexan-2-ones 7 and 8, carboxylic acid 9, gamma-lactone 10, cyclopentan-2-one 11, and esters 16 and 17. Structural correlations were unambiguously deduced from X-ray structure analyses of 7a, 9a, and 17a. The origin of facial diastereoselectivity with this class of organometallic electrophiles lies in steric and stereoelectronic biases rather than in purely electronic nucleophilicity. (c) Wiley-VCH Verlag GmbH & Co. KGaA.