Synthesis and Reactions of (2-Oxocyclobutyl)diphenylphosphine Oxide

Abstract

We succeeded in the synthesis of (2-oxocyclobutyl)diphenylphosphine oxide [4] via (1cyclobutenyptriphenylphosphonium salt [1] in good yield. Reaction of [4] with methanol gave methyl 4-(diphenylphosphinyl)butyrate [5] in 64% yield. Reaction of [4] with Schiff bases such as N-isobutylidenebenzylamine [6a], N-benzylidenebutylamine[6b], and N-benzylideneiso`proPylakriaine [6c] gave N-benzy1-5-(diphenylphosphiny1)-6-isopicipyl-2-pip e ridinone [7a] (28%), 4-(diphenylphosphiny1)-4-pentenamides [8a-c] (33-44%), and 4(diphenylphosphinyl)butyramides [9a, c] (24-32%), 'respectively. Reaction of [4] with diazomethane gave the ring-expansion products, (2-oxocyclopentyl)diphenylphosphine oxide (39-61%) and (2-methoxy-1-cyclopentenyl)diphenylphosphine oxide [11] (6-40%). Reaction of the enolate anion of the cyclobutanone [4]with diphenyl phosphorochloridate and benzoyl chloride produced enol esters of the cyclobutanone, [13] and [14], respectively, in good yields. Reaction of enol diphenylphosphate ester [13] with lithium dibutylcuprate ( I ) gave (2-butyl-1-cyclobutenyl)diphenylphosphine oxide CM) in 32% yield. The PielsAlder reactions of 3-substituted 2-diphenylphosphiny1-1, 3-butadienes, generated by thermolysis of (2-substituted 1-cyclobutenyl)diphenylphosphine oxides [14] and [15], with N-phenylmaleimide gave functionalized (1-cyclohexenyl)diphenylphosphine oxides [16] (28%) and [17](82%). Reaction of [4] with benzaldehyde did not give the Wittig-Horner reaction product, but 4-(diphenylphosphinyl)-5-phenyl-4-pentenoic acid [20] was obtained in 53% yield.