Rhodium(II)‐Catalyzed Inter‐ and Intramolecular Enantioselective Cyclopropanations with Alkyl‐Diazo(triorganylsilyl)acetates

The intermolecular cyclopropanation of styrene with ethyl diazo(triethylsilyl)acetate ( 1a ) proceeds at room temperature in the presence of chiral Rh II carboxylate catalysts derived from imide‐protected amino acids and affords mixtures of trans ‐ and cis ‐cyclopropane derivatives 2a in up to 72% yield but with modest enantioselectivities (<54%) ( Scheme 1 and Table 1 ). Protiodesilylation of a diastereoisomer mixture 2a with Bu 4 NF is accompanied by epimerization at C(1) (→ 3 ). The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetate ( 8a ), in turn, affords optically active 3‐oxabicyclo[3.1.0]hexan‐2‐one ( 9a ) with yields of up to 85% and 56% ee ( Scheme 3 and Table 2 ). Similarly, the (2 Z )‐pent‐2‐enyl derivative 8d reacts to 9d in up to 77% yield and 38% ee ( Scheme 3 and Table 3 ). In contrast, the diazo decomposition of (2 E )‐3‐phenylprop‐2‐enyl and 2‐methylprop‐2‐en‐1‐yl diazo(triethyl‐silyl)acetates ( 8b and 8c , resp.) is unsatisfactory and gives very poor yields of substituted 3‐oxabicyclo[3.1.0]hexan‐2‐ones 9b and 9c , respectively ( Table 3 ).