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

✍ Scribed by Paul Müller; Fabienne Lacrampe

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: German
• Weight: 241 KB
• Volume: 87
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.200490256

✦ Synopsis

Abstract

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).