We found that intramolecular [2+2] cycloaddition of simple allenenes and allenynes proceeded under thermal conditions to give strained bicyclic compounds bearing a cyclobutane framework. N-[(1S)-1-Alkyl-2,3-butadienyl]-2,4,6-trimethyl-N-[(E)-3-phenylprop-2-enyl]phenylsulfonamides and other related substrates regio- and stereoselectively undergo intramolecular [2+2] cycloaddition at the distal double bond of allene moiety in DMF at 150°C to produce (1R,4S,8S)-4-alkyl-3-aza-8-phenyl-3-(2,4,6-trimethylphenylsulfonyl)bicyclo[4.2.0]oct-5-enes in high yields as the sole isolable isomer. This simple and environmentally-benign process would extend the potential application of fused bicyclic cyclobutanes in synthetic and medicinal chemistry.
