Role of the methoxy group in product formation via TiCl4 promoted 4-phenyldioxolane isomerizations
Abstract
The product distribution obtained from the TiCl4 initiated intramolecular isomerizations of 4-
methoxyphenyl- and trimethoxyphenyldioxolanes at -78 oC, -30 oC and 0 oC provided insights
into the important regiochemical role played by these groups in such Mukaiyama- type
rearrangements through their resonance effects on the aryl ring of the dioxolanes.Our interest in naphthopyranquinones as potential antimicrobial and antibiotic agents has
extended over two decades1-6
as a result of their well documented importance.7,8 Additionally, the
synthesis of benzopyrans as model systems has received attention by ourselves6,9-13 and others.14-
16 Of particular interest to us was our earlier discovery of a TiCl4 - induced intramolecular
isomerization in which phenyl- and naphthyldioxolanes were stereoselectively transformed into
their corresponding benzo- and naphthopyrans.17