An improved synthesis of 1,2,3,4-tetrahydroisoquinolines via intramolecular cyclization of N-acyl-N-(aryl)methyl-2- (phenylsulfinyl)ethylamine by Pummerer reaction

Article abstract of DOI:10.1248/cpb.45.813

Pummerer reaction of the sulfoxides 5 of N-acyl-N-(aryl)methyl-2- (phenylthio)ethylamines (4) on treatment with trifluoroacetic anhydride (TFAA) effectively caused intramolecular cyclization under a mild condition to give N-acyl-4-phenylthin-1,2,3,4-tetrahydroisoquinolines (TIQs) (7). The reaction of the N-formyl sulfoxide 5c without a methoxy group in the benzene ring using a formyl group for N-protection is particularly efficient. Treatment of the N-formyl sulfoxide 5f with TFAA did not give away TIQ, but a sequential treatment using TFAA and BF₃·Et₂O afforded N-formyl-4- phenylthio-TIQ (7f) in quantitative yield. The efficiency of this method or preparing TIQs was demonstrated in the synthesis of 1,4-dideuterio-TQ (10D) and its N-methyl derivative (11D).

Full text of DOI:10.1248/cpb.45.813

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