O-Menthane

A mixture of o-menthanes resulted from reduction of o-cymene with Ca(NH3)6,297 and a neat route to the o-menthane skeleton involved photochemical addition of allene to 3-methylcyclohex-2-en-l-one and opening of the cyclobutyl ring with BF3.298 O-Menthadi- and tri-enes resulted from pyrolysis of verbenene.299 Acid-and base-promoted isomerizations of o-menthadienes300 and dehydration of cis- and trans- o-menthan-8-ols with a variety of reagents have been recorded.301 Optically active 2-methyl-4-isopropenylcyclohexanone (which is a useful precursor for ra-menthane derivatives) has been prepared by pyrolysis of chiral 2,2,5-trimethyl-bicyclo[3.1.1 ]heptan-2-one.302... 

There is still little synthetic work toward the main terpenes of the o-menthane group (see Vol. 4, p. 527). Synthesis of the methyl ether 683 and its isomer 684 from, respectively, 2-methoxy-6-methylbenzoic acid and 3-methoxy-2-methylbenzoic acid showed that e substance isolated by Bohlmann from Piqueria trinervia was 683, and not 684, as he had believed. ... 

Baccharis genistelloides, from which carquejol is obtained, is not the only Baccharis species to yield an o-menthane. Bohlmann and Zdero have isolated two esters of the type (190) from Baccharis timera ... 

Besides p-menthane derivatives discussed above, there are a few other isoprenoid cyclohexane types with rather limited distribution. Some of these have been found to occur in woody tissues also - e.g., 73, an o-menthane derivative. 

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