Physical Image vs. Structure Relation. 9. Synthesis and Structural Study of Some 2,5-Bis-alkoxysubstituted 3-Oxolenes and Oxolanes: An Experimental and Theoretical Approach

Two 2,5-bis-substituted 3-oxolenes 2 stable only in anhydrous, acid-free solutions were obtained in the Clauson-Kaas reaction. An immediate catalytic hydrogenation of the E/Z isomeric mixture of oxolene 2a, followed by chromatography, afforded one geometrical form of oxolane diol 4 (isomer I), which was subsequently submitted to several attempts of cyclization to an unknown bis-spiroacetal of succinic anhydride (6). A rationalization of this process failure and the Z geometry of product I exhibiting interesting spectroscopic features were inferred from theoretical results (HF/6-31G** calculations) and experimental data for solution (NMR, IR). Some additional ab initio GIAO-CPHF NMR computations concerning relevant model bis-acetals 3 and 5 were performed, as well.