Brønsted acid catalyzed intramolecular benzylic cyclizations of alkylpyridines
作者:Ashabha I. Lansakara、Daniel P. Farrell、F. Christopher Pigge
DOI:10.1039/c3ob42039f
日期:——
incorporated into the side chains of 2- and 4-alkylpyridines participate in intramolecular aldol-like condensations with pyridine benzylic carbons in the presence of Brønstedacid catalysts. Pyridines featuring β-ketoamide side chains undergo cyclization in the presence of 10 mol% TfOH to afford pyridyl-substituted hydroxy lactams in good yield. These products were found to be resistant to further dehydration
Intramolecular Cyclization Manifolds of 4-Alkylpyridines Bearing Ambiphilic Side Chains: Construction of Spirodihydropyridines or Benzylic Cyclization via Anhydrobase Intermediates
作者:Sharavathi G. Parameswarappa、F. Christopher Pigge
DOI:10.1021/jo301247c
日期:2012.9.21
side chains have been converted to spirodihydropyridines upon treatment with ethyl chloroformate and sub-stoichiometric amounts of Ti(OiPr)4. Alternatively, inclusion of mild base in the reaction medium was found to facilitate generation of anhydrobase intermediates. Subsequent aldol-like condensations with electrophilic side chain moieties followed by hydrolysis delivered benzylically cyclized pyridines
在用氯甲酸乙酯和亚化学计量的Ti(O i Pr)4处理后,具有亲核β-二羰基侧链的4-烷基吡啶已转化为螺二氢吡啶。或者,发现在反应介质中包含温和的碱有助于促进脱水碱中间体的产生。随后与亲电子侧链部分的醛醇状缩合,然后水解,以高收率递送苄基环化的吡啶。环化脱水碱中间体的原位氢化得到4-取代的哌啶。