Rhodium-catalyzed synthesis pyridones

The dipolar cycloaddition chemistry of isomiinchnones is a powerful and concise route to polycyclic azaheterocycles, and Padwa has been the pioneer in this effort. Sheehan and Padwa (159) employed the rhodium-catalyzed isomiinchnone generation and subsequent trapping to a synthesis of 2-pyridones and the alkaloid... 

The dipolar cycloaddition chemistry of isomunchnones is a powerful and concise route to polycyclic azaheterocycles, and Padwa has been the pioneer in this effort. Sheehan and Padwa employed the rhodium-catalyzed isomunchnone generation and subsequent trapping to a synthesis of 2-pyridones and the alkaloid ( )-ipalbidine (465) (Fig. 4.144). Thus ot-diazo imide 462 was readily constructed from 2-pyrrolidinone and allowed to react with rhodium acetate in the presence of c/i-l-(phenylsulfonyl)-l-propene to afford 2-pyridone 464 after loss of phenylsul-finic acid. Further manipulation, featuring a Stille coupling, gave ( )-ipalbidine 465. 

Rhodium-catalyzed [2+2+2] cycloadditions for the synthesis of substituted pyridines, pyridones, and thiopyranimines 13H(87)1017. Synthesis of six-membered azaheterocycles by means of the P-lactam synthon method 13MR01. 

The rhodium-catalyzed chemo-, regio- and enantioselective [2-1-2- -2] cycloaddition of unsymmetrical alkynes to isocyanates leads to a wide range of 2-pyridones [123]. This method is used satisfactorily in the synthesis of axially chiral arylpyridones 2.196 by coupling alkylisocyanates with unsymmetrical a,to-diynes 2.195 that have one o-substituted phenyl group in one acetylene branch and terminal triple bond in another (Scheme 2.68) [123],... 

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