A new approach to helical primary structures of four-membered rings: (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane

A new approach to helical primary structures of four-membered rings uses a cycloaddition of a trimethylenketeniminium salt to suitable tailored methylenecyclobutanes to assemble the desired carbon framework. The results are short and effective syntheses of (M)-trispiro3.0.0.3.2.2]tridecane (M)-5], and (P)- and (M)-tetraspiro3.0.0.0.3.2.2.2]hexadecane (P)- and (M)-24]. Unlike helices of three-membered rings, the specific rotation decreases, as the length of the helix increases.