Benzocyclobutenes isochroman-3-ones

An investigation established a relationship between the intensity of the [M - C02] ion in the spectra of substituted isochroman-3-ones (29) and the yield of the corresponding benzocyclobutene (29a), obtained from flash vacuum pyrolysis of (29 equation 5) (77JOC2989). 

Fukumoto et al have taken advantage of the propensity for inward rotation of an acyl group to prepare the isochroman-3-one (36), an intermediate in their synthesis of geneserine, a constituent of the calabar bean. The conversion of the benzocyclobutene (37) to (36) proceeds via ring opening to the o-quinodimethane (38) followed by cyclization and a 3,3-sigmatropic rearrangement. 

A, few isochroman-3-ones occurs in nature The importance of isochroman-3-ones however is because they are valuable intermediates for the synthesis of isoquinolines. A most interesting use of isochroman-3-ones is that they provide benzocyclobutenes which are valuable synthons for berbines, spiro-benzylisoquinolines, 3-aryl isoquinoline, benzophenanthridines, benzocarbazoles, yohimbin, tetracycline, steroids etc. 

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