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.
“…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.…”
Reaction of readily available a-(benzotriazolyl)alkyl urea derivatives (derived from aromatic, heteroaromatic, and aliphatic aldehydes) with b-keto esters resulted in 3,4-dihydropyrimidin-2(1H)-ones in good to excellent yields.
“…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.…”
Reaction of readily available a-(benzotriazolyl)alkyl urea derivatives (derived from aromatic, heteroaromatic, and aliphatic aldehydes) with b-keto esters resulted in 3,4-dihydropyrimidin-2(1H)-ones in good to excellent yields.
“…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).…”
A TMSOTf-promoted cycloaddition of N-benzoyl-N,Oacetals with allyl silanes to synthesize silicon-containing oxazines with high diastereoselectivities has been developed. The obtained products might be useful as building blocks in organic synthesis.
The intramolecular bromoamination of allylated aldoxime ethers leads first to isoxazolidinium salts which then undergo a skeletal rearrangement to form bromo-5,6-dihydro-4H-1,3-oxazines. Aliphatic aldoxime ethers with α-protons undergo multiple brominations before rearrangement.
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