A synthesis of 3-phenyl-1,2,3,4-tetrahydroisoquinoline and 2-phenyl-1,2,4,5-tetrahydro-3H-3-benzazepine via Pummerer-type cyclization: enhancing effect of boron trifluoride diethyl etherate on the cyclization

Pummerer Synthesis of Chromanes Reveals a Competition between Cyclization and Reductive Chlorination

The competition between an unprecedented reductive chlorination and the Pummerer reaction was studied and applied to the synthesis of benzofused oxygen heterocycles including 3-aminochromanes and in the intramolecular chlorination of activated aromatic rings. The use of (COCl)₂ as a Pummerer activator showed substantial activity, producing α-chlorinated sulfides that can undergo Pummerer-Friedel-Crafts cyclization. If the aromatic ring has electron-donating groups in position three, then the reaction follows a different pathway, yielding the reductive chlorination products, where the chlorine atom comes from a sulfonium salt.

Pummerer Cyclization Revisited: Unraveling of Acyl Oxonium Ion and Vinyl Sulfide Pathways

Two viable pathways (vinyl sulfide and acyl oxonium ion) for the Pummerer cyclization have been unraveled that expand the reaction scope and capabilities. Use of Brønsted- enhanced Lewis acidity was key to realization of the vinyl sulfide pathway, whereas selective complexation of the sulfur lone pair facilitated the unprecedented acyl oxonium ion pathway. Preliminary mechanistic investigations support these hypotheses. A range of substrates have been explored to understand the reaction parameters.

Synthesis and in vitro cytotoxicity of 1,2,3,4-tetrahydroisoquinoline derivatives

Several 1-alkyl-1,2,3,4-tetrahydroisoquinoline (TIQ) derivatives, which may play a role in Parkinson's disease, have been synthesized via Pummerer-type cyclization of the sulfonium ion formed in situ from N-formyl sulfoxide. Using an in vitro trypan blue exclusion assay, high concentrations of TIQ derivatives possessing bulky alkyl group substituents such as 1-cyclobutyl-, 1-cyclohexyl-, 1-phenyl- or 1-benzyl- at the C-1 position were found to significantly affect the viability of PC12 cells. Moreover, TIQ derivatives that moderately or strongly induced apoptosis (e.g., 1-phenyl-TIQ and 1-cyclohexyl-TIQ, respectively) paralleled the results obtained using the trypan blue exclusion assay. These results suggest that the size and electron-donating properties of functional groups may affect the cytotoxicity of TIQ derivatives.

Alkaloidal constituents of Mucuna pruriens seeds

The seeds of Mucuna pruriens (L.) DC. after chemical analysis afforded four tetrahydroisoquinoline alkaloids which have been isolated for the first time from M. pruriens. Out of them, two are new whose structures have been elucidated by spectroscopic methods.