Reaction of thioamides (e.g., II) with benzynes generated by the hexadehydro-Diels-Alder (HDDA) cycloisomerization (e.g., I) produces dihydrobenzothiazines (e.g., III). It is postulated that the reaction proceeds via benzothietene (cf. IV) and o-thiolatoaryliminium (cf. V) intermediates and that the latter undergoes intramolecular 1,3-hydrogen atom migration to produce the penultimate isomeric iminium zwitterions VI.
Bibliographical noteFunding Information:
Support for this research was provided by the National Institutes of General Medical Sciences of the U.S. Department of Health and Human Services (GM65597). V.P. appreciates support from a Gleysteen?Heisig fellowship for undergraduate students. Some of theNMRdata were obtained with an instrument acquired with funds from the NIH Shared Instrumentation Grant program (S10OD011952).
© 2016 American Chemical Society.