Preparation of New Nitrogen-Bridged Heterocycles. 15. Synthesis and Reaction of 1,9a-Dihydropyrido[2,1-c][1,4]thiazines

• Published in: Bulletin of the Chemical Society of Japan Vol. 60; no. 5; pp. 1867 - 1879
• Main Authors: Kakehi, Akikazu, Ito, Suketaka, Yonezu, Shingo, Maruta, Katsunori, Yuito, Kazuhiro, Shiohara, Morio, Adachi, Kyoko
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.05.1987; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.60.1867

Alkaline treatment of 1-[2-(substituted methylthio)vinyl]pyridinium bromides, readily obtainable from the S-alkylation of pyridinium 1-(thiocarbonyl)methylides with various alkyl bromides such as bromoacetonitrile, ethyl bromoacetate, and some phenacyl bromides, gave smoothly 1,9a-dihydropyrido[2,1-c][1,4]thiazine derivatives as almost isomeric mixtures. These dihydropyridothiazines are very unstable and decomposed rapidly at ordinary temperature, but by treating them with a dehydrogenating agent such as lead tetraacetate (LTA) or 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) at 0 °C the desulfurized and the rearranged aromatic indolizine derivatives were formed in moderate to good yields.