Rhodium‐Catalyzed Asymmetric Nitroallylation of Arylmetallics with Cyclic Nitroallyl Acetates and Applications in Organic Synthesis

Highly enantioselective rhodium‐catalyzed nitroallylations of arylboronic acids and arylzinc chlorides with cyclic nitroallyl acetates are described. Catalyst screening indicated that the rhodium complex of [Rh(OH)(COD)]2 and optically pure binap is the optimal catalyst for the nitroallylation of arylboronic acids with 2‐nitrocyclohex‐2‐enyl esters, providing good yields and high enantioselectivities of up to 99 % ee. The rhodium complex prepared from Rh(acac)(C2H4)2 and (R)‐binap efficiently catalyzed the nitroallylation of arylzinc chlorides with 2‐nitrocyclohex‐2‐enyl acetate at 0 °C in high yields of up to 93 % and with high enantioselectivities of up to 96 % ee. A number of synthetically useful intermediates with high optical purity were prepared with this reaction as starting point: concise total syntheses of optically pure (+)‐β‐lycorane in 53 % overall yield and of (+)‐γ‐lycorane in 52 % overall yield were achieved by commencing with the asymmetric nitroallylation of 3,4‐methylenedioxyphenylzinc chloride with 2‐nitrocyclohex‐2‐enyl acetate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)