Stereochemical aspects of novel 5,6-dihydro-4H-1,3-oxazines

Abstract

Novel polysubstituted 5,6-dihydro-4H-1,3-oxazines are synthesized by 1,4-cycloaddition of unactivated olefins with N-acyliminiums from benzotriazole precursors. The configuration and conformation of the products are deduced from NMR investigation. The regio-and exo-endo stereochemistry of the cycloaddition are discussed. Conformations of compounds of six types of substitution (6-mono; 6,6-, 5,6-and 4,6-di; 4,6,6-and 4,5,6-tri) are rationalized on the basis of axial-1,3-repulsion and the anomeric effect.

Expedient Synthesis of Biginelli-Type Dihydropyrimidinones Using α-(Benzotriazolyl)alkyl Urea Derivatives

“…Benzotriazole has been emphasized as a new synthetic auxiliary that offers many advantages. 29 N-(a-Amidoalkyl)benzotriazoles have been used as powerful reagents for the N-amidoalkylation of amines, 30 Oamidoalkylation of alcohols, 31 S-amidoalkylation of mercaptans, 32 and C-amidoalkylation of CH-acidic, 33 electron-rich aromatic compounds, 34 and deactivated olefins. 35 This offered some clues that reaction of a-benzotriazolated urea with a b-keto ester could be a possible modification of the Biginelli reaction that produces high yields of the target dihydropyrimidines.…”

A Highly Diastereoselective Access to Silicon-Containing Oxazines via the TMSOTf-Promoted Reactions of N-Benzoyl-N,O-acetals with Allyl Silanes

“…The NOE between H 4 and two protons of the CH 2 TMS group and between H 6 and the ortho proton of the phenyl ring demonstrated the trans relationship of the two substitutents at the 4-and 6-positions of the oxazine ring. 11 Other acids such as TiCl 4 , BF 3 •OEt 2 , Bu 2 BOTf, TsOH, TMSOTf, and TBSOTf were also screened. Among them, TMSOTf gave rise to the best results in terms of the yield of 13a (74%) and the trans/cis ratio (10:1).…”