Cyclization of isoprenoid compounds Communication 8. Mechanism of the stereospecific cyclization of geranylacetone
Under conditions varying over a wide range steric orientation in the cyclization of geranylacetone into a chromene does not change. The reaction goes stereospecifically under all the conditions studied, if secondary isomerization processes are excluded.
The nonstereospecificity of the cyclization of geranylacetone in presence of BF3 may be explained by the ready mutual isomerization of the cis and trans chromenes under the conditions of the experiment.
A scheme is proposed for the mechanism of the reaction: according to this the stereospecific cyclization of geranylacetone proceeds by the simultaneous closing of both rings with trans-addition at the 6,7-double bond.
It is suggested that one possible prerequisite for the occurrence of the stereospecific cyclization of isoprenoids is the presence in the molecule of a nucleophilic group that is able to ensure simultaneous addition at the double bond and determine the configuration of the compound obtained.
KeywordsChromene Double Bond Isoprenoids Isoprenoid Simultaneous Addition
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