Recent studies on the synthesis of homocyclic systems
This paper constitutes a report of results that have been obtained in a new programme of study which has been under way for some time in our laboratory. The ultimate aim of this research is to develop a laboratory method of simulating the cyclization processes that are involved in the biosynthesis of the polycycloisoprenoids such as the tetraand penta-cyclic triterpenoids as weil as the steroids. This programme is only in its preliminary stages, and our results thus far are limited almost exclusively to relatively simple systems. I t has been unequivocally established 1 by the work of Bloch, Cornforth, Tavormina, Woodward and others that the biosynthesis of lanosterol and, in turn, of cholesterol from mevalonic acid involves an in termediary openchain polyolefin, namely squalene (I), which undergoes cyclization and rearrangement. I t seems probable that the vast nurober of polycyclotriterpenoids occurring in nature are also derived from squalene. In 1955 both StorkZa and Eschenmoser3 proposed a stereo-rational theory for the biogenesis of most of the known members of this group of natural pro-