Conformation analysis of spiranes by the force-field method. Part 1. Chirality and diastereoisomerism of spiro-compounds: spiro[5.5]undecane and derivatives

Abstract

In Cahn, Ingold, and Prelog's classification of chiral molecules, chirality of spiranes was analysed in terms of an unformulated assumption of planarity of molecular rings on the basis of rapid inversion. On this assumption (which remained unformulated and was never abandoned) the hydrocarbon skeleton is achiral, and chirality can be generated by appropriate substitution. Thus, the chirality of unsubstituted spiranes has been overlooked. A general condition for chirality of unsubstituted spiranes is given, and some examples of the manifestation of chirality of spiro[5.5]undecanes are discussed in detail. In particular, the diastereoisomerism of spiro[5.5]undecanes substituted at positions 1 and 5, and that of dispiro[5.2.5.2]hexadecane resulting from the chirality of the spiro atoms, are analysed on the basis of molecular mechanics calculations.