Hetero-Diels–Alder reactions of hetaryl thiochalcones with acetylenic dienophiles

ABSTRACT

Hetaryl-substituted thiochalcones react with acetylenic mono- and diesters in the THF solution in the presence of LiClO₄ at 65°C to give, after 24 h, 4H-thiopyran carboxylates and dicarboxylates, respectively, in moderate to good yields. The same reactions were performed also in the THF solution without a catalyst under microwave irradiation. In that case, the reaction time was reduced to three minutes and, in most cases, an improvement in the yield of the [4+2]-cycloadduct was observed. The reactions with methyl propiolate occurred regioselectively and the 3-carboxylates were formed exclusively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Chalcones
• thiochalcones
• acetylenic dienophiles
• hetero-Diels–Alder reactions
• 4H-thiopyrans
• microwave irradiation

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Science Center (Cracow, Poland) within the project Maestro [grant number: Dec-2012/06/A/ST5/00219].