Efficient and regioselective chromium(0)-catalyzed reaction of 2-substituted furans with diazo compounds: stereoselective synthesis of (2 E,4 Z)-2-aryl-hexadienedioic acid diesters

Abstract

Pentacarbonyl(η 2- cis-cyclooctene)chromium(0) ( 1) catalyzes efficiently reactions of diazo compounds with electron-rich furans. The reaction of 2-methoxyfuran ( 2) with alkyl α-diazoarylacetate ( 3a– g) furnishes the (2 E,4 Z)-2-aryl-hexadienedioic acid diesters ( 4a– g) in excellent yields. These reactions are highly regioselective. The cyclopropanation intermediates formed from 1 and diazo compounds 3a– g always arise from a carbene addition to the less substituted C C bond of 2. The resulting cyclopropanation product undergoes a ring opening reaction to form the corresponding (2 E,4 Z)-2-aryl-hexadienedioic acid diesters ( 4a– g). The pentacarbonylchromium(0)-catalyzed reactions of 2-alkylfuran ( 5a– b) with ethyl α-diazophenylacetate ( 3a) and 9-diazo-9 H-fluorene ( 3h) produce the 1( E),3( E)-butadienes ( 6a– d) in very good yields.