Crystal structures of three cyclohexane-based γ-spirolactams: determination of configurations and conformations

Abstract

The title compounds, 2-azaspiro[4.5]deca-1-one, C 9 H 15 NO, ( 1a ), cis -8-methyl-2-azaspiro[4.5]deca-1-one, C 10 H 17 NO, ( 1b ), and trans -8-methyl-2-azaspiro[4.5]deca-1-one, C 10 H 17 NO, ( 1c ), were synthesized from benzoic acids 2 in only 3 steps in high yields. Crystallization from n -hexane afforded single crystals, suitable for X-ray diffraction. Thus, the configurations, conformations, and interesting crystal packing effects have been determined unequivocally. The bicyclic skeleton consists of a lactam ring, attached by a spiro junction to a cyclohexane ring. The lactam ring adopts an envelope conformation and the cyclohexane ring has a chair conformation. The main difference between compound 1b and compound 1c is the position of the carbonyl group on the 2-pyrrolidine ring with respect to the methyl group on the 8-position of the cyclohexane ring, which is cis ( 1b ) or trans ( 1c ). A remarkable feature of all three compounds is the existence of a mirror plane within the molecule. Given that all compounds crystallize in centrosymmetric space groups, the packing always contains interesting enantiomer-like pairs. Finally, the structures are stabilized by intermolecular N–H···O hydrogen bonds. Electronic supplementary material The online version of this article (10.1186/s13065-019-0586-7) contains supplementary material, which is available to authorized users.