Pyridone, axially chiral

The Rh(I)/dppf complex-catalysed 2-i-2-i-2-cycloaddition of oximes and diynes formed substituted pyridines in moderate to good yields (88%), under mild conditions. A one-pot procedure has been developed using aldehydes.The Ni-catalysed 2 -I-2 -I-2-cycloaddition of isocyanates (117) with 1,3-dienes (118) in MeCN produced 6-substituted dihydropyrimidine 2,4-diones (119). A key intermediate in this reaction is a five-membered azanickelacyclic species (Scheme 35). " The enantioselective cationic Rh(I)-catalysed 2-i-2-i-2-cycloaddition of diynes and isocyanates formed axially chiral pyridones with high ees (82%). The unique source of chirality is provided by a system containing [Rh(cod)Cl]2, l,4-bis(diphenylphosphino)butane, and the silver phosphate salt Ag(5)-TRIP. " " The Rh-catalysed 2-I-2-I-2-cycloaddition of diynes to sulfonimines in DCE, at r.t. to 80 °C, yielded 1,2-dihydropyridines in good yields (54-86%) and enantioselectivity (61-96%... 

Axially chiral A/-aryl-2-pyridone 55 was obtained by the reaction of a,w-diyne 7 with o-substituted aryl isocyanate (Scheme 5.19) [34]. BINAP was an efficient ligand for enantioselective cycloaddition to give axial chirality. 

On the other hand, the neutral iridium(I) catalyst is also effective for construction of the C—N axial chirality. In 2012, Takeuchi et al. reported that the reactions of malonate-linked internal 1,6-diyne 29 with ortho-substituted phenyl isocyanates 30 in the presence of the neutral iridium(I)/BINAP or Hg-BINAP catalyst furnishes enantioenriched A-aryl-2-pyridones 31, having a chiral C—N axis, with good yields and ee values (Scheme 9.12) [14]. 

Axially chiral pyridines as well as axially chiral pyridones could be synthesized via rhodium-catalyzed enantioselective [2 + 2 + 2] cycloaddition. The reaction of 1,6-diyne 68 with ethyl cyanoformate (69) in the presence of the cationic rhodium(I)/Segphos catalyst furnished axially chiral arylpyridine 70 as a single regioi-somer with excellent ee value (Scheme 9.25) [19],... 

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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