We report the one-pot synthesis of 4-amino thiochromans using simple aminocyclopropanes and thiophenols through a formal [3+3] annulation reaction. This reaction proceeds under mild conditions with good functional group tolerance. The thiochroman core was formed with complete regioselectivity, and modification of complex drug molecules containing an aminocyclopropane was also realized.

We describe different modes of dimerization of various α′,γ-dioxyenone derivatives with potential applications to the synthesis of high-order securinega alkaloids. We learned that the relative stereochemical relationship between α′- and γ-hydroxyl groups of the α′,γ-dihydroxyenone derivative determines the mode of dimerization. While cis-α′,γ-dioxyenone 26 provided the Rauhut–Currier-type (RC-type) dimer 31 upon reaction with TBAF, trans-α′,γ-dihydroxyenone 34 afforded dimeric tetrahydrofuran derivative 41 under the same reaction conditions. We also noticed that the protection of the γ-hydroxyl group drastically changes the reaction outcomes. While cis-α′-oxy-γ-OPiv-enone 49 did not show any reactivity in the presence of TBAF, trans-α′-hydroxy-γ-OPiv-enone 45 produced the RC-type dimer 46 under the same reaction conditions. Computational analysis revealed the detailed mechanism of the latter transformation.

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