Synthesis of β-Lactams by the Cycloaddition of 2, 3-Dihydrofuran to Isocyanates

Abstract

The [2+2]cycloaddition of 2, 3-dihydrofuran (1) to phenyl isocyanate (2a) at 100° C for 20 h gave bicyclic β -lactam, 7-phenyl-2-oxa-7-azabicyclo[3.2.0]heptan-6-one (3a) with 86% yield. The reaction gave a good result when the reaction was carried out in the absence of catalyst in nonpolar solvent. The [2+2]cycloaddition of 1 to various aryl isocyanates at 100° C for 20 h gave corresponding bicyclic β -lactams in high yield and selectivity, however, the reactions of 1 with alkyl isocyanates and of other vinyl ethers with 2a did not occur. A concerted mechanism was supposed on the [2+2]cycloaddition of 1 to 2a.