Cycloaddition Reactions of Neutral 2-Azadienes with Enamines − Regiospecific Synthesis of Highly Substituted Dihydropyridines and Pyridines

Abstract

2115ization of heterodienes gives pentasubstituted 2,3-dihydropyridines and pyridines in a regioselective fashion.this context, we have been involved in the synthesis of neutral [11] and electron-poor azadienes [9] as well as in the preparation of nitrogen-heterocyclic compounds. [5a,5c,14] As a continuation of our work on the [4ϩ2] cycloaddition chemistry of 2-azadienes, we aim here to explore a new and effective strategy for the preparation of pyridine derivatives through dimerization of electronically neutral 2-azadienes and their reaction with enamines.

Diverse Reactivity in a Rhodium(III)‐Catalyzed Oxidative Coupling of N‐Allyl Arenesulfonamides with Alkynes

“…Subsequent oxidative aromatization furnishes the final product of a formal oxidative 1,3-shift of the sulfonyl group. [14] We carried out cross-over experiments to probe the intermolecularity of the sulfonyl 1,3-shift (Scheme 3 c). [15,16] When an equimolar mixture of 4 ae and 4 bf was heated at 130 8C under the catalytic conditions, the four expected products 3 ae, 3 af, 3 be, and 3 bf were detected by GC in a 1.1 : 1.4 : 1 : 1.1 ratio, which is consistent with our proposed mechanism.…”

Cascade aza-Wittig/6π-Electrocyclization in the Synthesis of 1,6-Dihydropyridines

“…Furthermore, a pericyclic fashion was employed as an additional strategy to access these scaffolds. Palacios and co-workers have reported the synthesis of 1,2-dihydropyridines through a [4 + 2] cycloaddition reaction of 2-azadienes (readily prepared by aza-Wittig reactions) and enamines (Scheme b) . Tejedor et al has developed a convenient domino access to substituted alkyl 1,2-dihydropyridine-3-carboxylates from propargyl enol ethers and primary amines by means of a Claisen rearrangement/isomerization/amine condensation/6π-aza-electrocyclization process (Scheme c) .…”

“…Palacios and co-workers have reported the synthesis of 1,2-dihydropyridines through a [4 + 2] cycloaddition reaction of 2-azadienes (readily prepared by aza-Wittig reactions) and enamines (Scheme 1b). 10 Tejedor et al has developed a convenient domino access to substituted alkyl 1,2dihydropyridine-3-carboxylates from propargyl enol ethers and primary amines by means of a Claisen rearrangement/ isomerization/amine condensation/6π-aza-electrocyclization process (Scheme 1c). 11 Very recently, Yu, Zhou et al reported the enantioselective synthesis of 1,2-dihydropyridines, using a chiral amine catalyst.…”

Iron-Mediated One-Pot Synthesis of 3,5-Diarylpyridines from β-Nitrostyrenes

“…However, 3,5-disubstituted pyridines have also been constructed through the multicomponent cyclization of small molecules. − In 1953, Eliel and co-workers, while studying the synthesis of the alkaloid papaverine, were able to condense homoveratric aldehyde with ammonia. Instead of papaverine, they isolated a new compound characterized as 3,5-bis­(3,4-dimethoxyphenyl)­pyridine.…”