Pd-Catalyzed [4 + 2] cycloaddition of methylene cyclic carbamates with dihydropyrazolone-derived alkenes: synthesis of spiropyrazolones

Abstract

In this paper, a palladium-catalyzed [4 + 2] cycloaddition of 5-methylene-1,3-oxazinan-2-ones with 4-arylidene-2,4-dihydro-3H-pyrazol-3-ones has been developed to produce spiropyrazolones in high yields with excellent diastereoselectivities in nearly all cases. The cycloaddition reaction was scaled-up without significant loss of yield, and its synthetic utility has been demonstrated by further transformations of the products. The reaction type of N–Ts cyclic carbamates under palladium catalysis was extended to include [4 + 2] cycloaddition for the first time.