FORMAMIDINES IN SYNTHESIS - AN EFFICIENT ONE-POT SYNTHESIS OF 7-SUBSTITUTED INDOLINES VIA INTRAMOLECULAR CYCLIZATION OF (2-PHENETHYL)FORMAMIDINES - AN ASYMMETRIC ROUTE TO BENZOPYRROCOLINE ALKALOIDS

o-Chloro-beta-phenethylamines, transformed into the N-tert-butylformamidines, were found to be excellent precursors to indolines following benzyne formation. A series of methoxy-substituted o-chlorophenethylamines containing an N-alkyl or aryl substitutent were subjected to sec-butyllithium producing the ortho-lithiated aromatic which subsequently lost lithium chloride at temperatures ranging from -78 to -50-degrees-C. The resulting benzyne was intramolecularly trapped providing the titled heterocycles. Quenching the reaction resulted in elimination of the tert-butyl isocyanide (isolated after aqueous workup as tert-butylformamide) and protonation (or alkylation) of the 7-lithio position. Overall the yields for this process were 60-95% for a variety of N-substituted phenethylamines. In addition, a one-pot total asymmetric route to benzopyrrocoline alkaloids was featured using this benzyne trapping of chiral formamidines.