Sulfone reagents in organic synthesis. Part 4. [2 + 2]-Cycloadditions of ynamines with .alpha.,.beta.-unsaturated sulfones: approach to versatile four-membered carbocyclic intermediates
Sulfone reagents in organic synthesis. Part 4. [2 + 2]-Cycloadditions of ynamines with .alpha.,.beta.-unsaturated sulfones: approach to versatile four-membered carbocyclic intermediates