SYNTHESIS OF BETA-LACTAMS BY THE CYCLOADD ITION OF 2,3-DIHYDROFURAN TO ISOCYANATES

The [2+2]cycloaddition of 2,3-dihydrofuran (1) to phenylisocyanate (2a ) at 100 degrees C for 20 h gave bicyclic beta-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 cat alyst in nonpolar solvent. The [2+2]cycloaddition of I to various aryl isocyanates at 100 degrees C for 20 h gave corresponding bicyclic bet a-lactams in high yield and selectivity, however, the reactions of 1 w ith 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.