Isoprene chromanes from

Chromans.—The use of isoprene in the synthesis of chromans from phenols is a well known reaction but one which is fraught with difficulties since regiochemical control is poor, In a re-examination of the problem Sartori et al have found... 

Chromenes.- Continuing interest in the precocenes and their biological action has stimulated further work on their synthesis. Precocene III (82) has been synthesized from a phenol, 3-methylbut-2-enal and titanium(IV) ethoxide93 and precocenes I and II were obtained by cyclization of the relevant 3-methoxyphenol with isoprene and dehydrogenating the resultant chroman with DDQ.94 Several new positional isomers of precocenes and related compounds have been synthesized and screened for insecticidal activity in a rice crop. Chromanones [such as (83)] were reduced with LAH to the chromanol which was efficiently dehydrated with a trace of toluene-4-sulphonic acid. Under some conditions, reduction gave dimeric... 

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