Intramolecular 4 + 3 cycloadditions. Further studies of (trimethylsilyl)methyl allylic sulfones

The scope of application of allylic sulfones in the 4 + 3 cycloaddition reaction was explored through analyzing the principles involved in the synthesis of (trimethylsilyl)methyl allylic sulfones. Treatment of a trimethylsulfone with trimethylaluminum indicated that simple butadienes did not trap the intermediate cation very efficiently. This was secondary to the inherently lower nucleophilicity of the butadiene in relation to the furan. It was also indicated that the minor product in an intramolecular 4 + 3 cycloaddition yielded a product containing a cis ring fusion.