Hydroboration. 70. The polycyclic hydroboration of acyclic and cyclic trienes with borane in tetrahydrofuran and triethylamine-borane. Reexamination of the stereochemistry of isomeric perhydro-9b-boraphenalenes
Treatment of unsaturated acid 1 with refluxing formic acid leads to an equilibrium mixture of lactones 2 and 3 in a ratio of 2:1. The stereostructure of γ-lactone 2 is secured by itssynthesisfrom epoxy-ester 6, the stereochemistry of which is deduced from reactivity arguments. The structure of δ-lactone 3 was proven by correlation with the trans-9-methoxy-10-methyl decalin 29, of unambiguous stereo-chemistry