Regioselective 1,3-dipolar cycloaddition reactions of 4-methylene-2-oxazolidinones with benzonitrile oxide

Substituted 4-methylene-2-oxazolidinones were prepared in two steps by cyclizing O-propargyl carbamates, which in turn were prepared from propargyl alcohols and phenyl isocyanate. The 4-methylene-2-oxazolidinones underwent a 1,3-dipolar cycloaddition reaction with benzonitrile oxide to give the corresponding spiro heterocycles. Where the substitution pattern on the oxazolidinone engendered facial asymmetry, the cycloadditon reaction proceeded with 5: 1 selectivity for the less hindered face of the dipolarophile.