[3+2] ANNULATION OF 2-SUBSTITUTED 3-NITRO-2H-CHROMENES WITH MERCAPTOACETALDEHYDE: STEREOSELECTIVE SYNTHESIS OF TETRAHYDRO-4H-THIENO[3,2-c]CHROMEN-3-OLS

Abstract

A diastereoselective method was developed for the synthesis of 4-trifluoromethyl- and 4-phenyl-substituted 3a-nitro-2,3,3a,9b-tetrahydro-4H-thieno[3,2-c]chromen-3-ols having cis configuration of substituents at the C-3, C-3a, C-4 atoms and the 9b-CH hydrogen atom from the available starting materials – 3-nitro-2H-chromenes and 2,5-dihydroxy-1,4-dithiane in 80–92% yields. This approach relied on a tandem of Michael and Henry reactions between 3-nitro-2H-chromenes and in situ generated mercaptoacetaldehyde in Et₂O at room temperature over 4–6 h, using Et₃N as catalyst.