AgOTf-Catalyzed Cycloisomerization of Alkynyl Oxiranes for Dihydro-1,4-oxazine Synthesis

Abstract

The efficient AgOTf-catalyzed isomerization reactions of various alkynyl oxiranes and alkynyl allyl alcohols were carried out at room temperature with moderate to good yields. This is an economical and mild method for the construction of O-heterocyclic compounds.

Key words

cyclization - isomerization - alkynes - epoxides - Lewis acids - silver - heterocycles - domino reaction

• References


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• 12 AgOTf-Catalyzed Cycloisomerization of Alkynyl Oxiranes for Dihydro-1,4-oxazine Synthesis; Typical Procedure: Alkynyl oxirane 1a (0.25 mmol) in anhydrous CH₂Cl₂ (0.2 M) was treated with a catalytic amount of AgOTf (10 mol%). The reaction mixture was stirred for 1 h at room temperature under a N₂ atmosphere. The progress of the reaction was monitored by TLC and, upon completion, the reaction mixture was concentrated and purified by silica gel column chromatography to afford the pure product 2a in 54% yield. ¹H NMR (300 MHz, CDCl₃): δ = 7.66 (d, J = 8.4 Hz, 2 H), 7.34 (d, J = 8.1 Hz, 2 H), 5.84 (s, 1 H), 4.93 (s, 1 H), 4.88 (s, 1 H), 3.82 (d, J = 12.8 Hz, 1 H), 3.31 (d, J = 9.0 Hz, 1 H), 2.83 (dd, J = 13.5, 9.3 Hz, 1 H), 2.44 (s, 3 H), 1.78 (s, 3 H), 1.64 (s, 3 H); ¹³C NMR (75 MHz, CDCl₃): δ = 143.9, 140.8, 140.4, 133.3, 129.8, 127.4, 113.4, 99.4, 74.3, 46.4, 21.6, 18.4, 17.8; HRMS (FAB): m/z [M⁺] calcd for C₁₅H₁₉NO₃S: 293.1086; found: 293.1035.