Relative stabilities and conformational ring inversion potentials in heterocyclic decalin systems and stereoelectronic implications

The energy differences between stereoisomers and the ring inversion potential surfaces of decalin (1) and various oxadecalins (2, 3), dioxadecalins (4-7), trioxadecalins (8, 9) and tetraoxadecalins (10, 11) were interrogated following the generally accepted scheme of a stepwise conformational six-ring inversion process and using molecular mechanics techniques (MM3 and MM3-GE, i.e. MM3 reparametrized for treatment of the "gauche effect"). The results were compared with some available experimental data and were also used to probe the validity of a recently elaborated protocol for ring-fragment analysis of oxygen-containing bicyclic systems in terms of their interannular fragment components: C-C-C-C, C-C-C-O, C-C-O-C, C-O-C-O-C and O-C-C-O, the latter two with their corresponding stereoelectronic effects, namely, the "anomeric effect" and the "gauche effect", respectively.