Synthesis of Thiazinoimidazoles by Lewis Acid–Catalyzed [3+3] Cycloaddition Reactions of Propargyl Alcohols with 2‐Mercaptoimidazoles

Abstract

The unique ytterbium‐catalyzed generation of sulfur‐ and selenium‐substituted propargylic and allenic cations and their reactions with 2‐mercaptoimidazole derivatives were described. The regioselective [3+3] annulation reactions proceeded to give a wide variety of S,N‐acetal‐containing bicyclic and tricyclic thiazinoimidazoles in good to high yields. Treatment of thiazinoimidazoles with LDA readily underwent ring contraction to afford thiazolobenzimidazoles. Deselenenylation and successive functionalization broaden the scope of accessible thiazinoimidazoles.

Thioalkynes in Ring Forming Reactions

“…Notably, this report was the first example of metallapyridine, which was prepared under mild conditions. Besides these above organic cyclic compounds synthesized successfully from thioalkynes, other organic cycles such as seven-membered silacyclic skeleton, [87] phenanthrenes, [88] thiazinoimidazoles, [89] cyclobutene-fused norbornadiene [90] and 2-vinylthiophenes [91] were also obtained facilely from thioalkynes. Notably, thioalkynes could be also applied to synthesize (À )-grandisine B, [92] fredericamycin A, [93] as well as 6''-(Z)and 6''-(E)-fluoro analogues of anti-hepatitis B.…”