6.pi.-Electrocyclization of 1-Azatrienes to 1,2-Dihydropyridines
作者:David F. Maynard、William H. Okamura
DOI:10.1021/jo00111a039
日期:1995.3
A series of alpha,beta-cis-dienals were synthesized by oxidation and then in situ isomerization of easily available beta-allenic alcohols. Subsequent reaction between the alpha,beta-cis-dienals and primary amines represents a simple and useful method for the direct preparation of 1,2-dihydropyridines. Reactivity profiles and activation parameters for the cyclization of alpha,beta-cis-dienimines are similar to those of the carbocyclic counterparts except the reaction is much faster. Despite the lack of a clear stereochemical label, the disrotatory nature of the ring closure is illustrated by the greater cyclization rates of 8'c and 8'd as compared to 7'c and 7'd, respectively. The observation that sterically more hindered systems (8'c and 8'd) cyclize faster than less hindered ones (7'c and 7'd) is a feature of 6 pi-electrocyclizations that is unprecedented.
Stereoselective Synthesis of (<i>E</i>)-β-Tributylstannyl-α,β-unsaturated Ketones: Construction of a Key Intermediate for the Total Synthesis of Zoanthamine
作者:Thomas E. Nielsen、David Tanner
DOI:10.1021/jo025902s
日期:2002.9.1
available from secondary propargylic alcohols via a two-step sequence involving highly regio- and stereoselective Pd(0)-catalyzed hydrostannation followed by mild oxidation (TPAP). The methodology has been applied to the synthesis of enantiomerically pure enone 12 which is a keyintermediate for the total synthesis of zoanthamine, a structurally complex marine natural product.