The intramolecular Buchner reaction of aryl diazoketones. Substituent effects and scope in synthesis

Abstract

Rhodium(II) acetate-catalysed cyclisation of α-diazoketones derived from 3-arylpropionic acid produces bicyclo[5.3.0]decatrienones or 2-tetralones depending on the substitution pattern of the aryl ring in the precursor; the former products are transformed into the latter catalytically with trifluoroacetic acid. Precursors with methyl, methoxy, and acetoxy substituents have been examined, efficient cyclisation occurring in all cases. When the precursor contains a meta-methoxy substituent, 2-tetralones are obtained directly. The efficient conversion of 3-phenylpropionic acid into trans-1-methylbicyclo[5.3.0]decan-2-one is also described, partial asymmetric synthesis having been realised through the use of rhodium (S)-mandelate as the cyclisation catalyst. Cyclisations of diazoketones derived from 4-phenylbutyric acid and 5-phenylpentanoic acid have also been studied; the former provides a new entry into the bicyclo[5.4.0]undecane system whereas the latter produces a 2,3-disubstituted cyclopentanone via C–H insertion. Aspects of the cycloheptatriene-norcaradiene equilibrium in fused ring systems are discussed.