Synthetic and computational studies on intramolecular [2+2] sulfonyl isocyanate-olefin cycloadditions

Novel unsaturated sulfonyl isocyanates were prepared using a boron trichloride promoted thermal cleavage of the corresponding sulfonylcarbamates. Due to their moisture sensitivity, the isocyanates were directly converted into sulfonylureas in good yields. An intramolecular cycloaddition of the olefinic sulfonyl isocyanates to give β-lactam-sulfonamide hybrids was not observed experimentally. Investigation of this cycloaddition by DFT-calculations using the 6-31G* and 6-311+G** basis sets showed it to be endergonic.