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

Abstract

AbstractThe intermolecular cyclopropanation of styrene with ethyl diazo(triethylsilyl)acetate (1a) proceeds at room temperature in the presence of chiral RhII 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 Bu4NF 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 (2Z)‐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 (2E)‐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).