2,3,4,4a, 5,6-Hexahydro-17/-pyrido

Methylation of 4,4a,5,6,7,8-hexahydro-3//-pyrido[l,2-c]pyrimidin-3-one (108, R = H) with methylmagnesium chloride in the presence of CU2I2 or Cu2Br2 gave l-methylperhydropyrido[l,2-c]pyrimidin-3-one 

A 1 2 mixture of isomeric cis-3,4a-H- and fra s-3,4a-H-3-methyl-2,3,4, 4a,5,6-hexahydro-l//-pyrido[l,2-a]quinazolines gave a 20 1 mixture in the presence of rhodium(II) acetate dimer and triphenylphosphine in ethyl acetate at 80°C for 20 h (94AJC1061). Epimerization probably occurs via a 10-membered ring intermediate (26). 

Treatment of betaine 341 with sodium propoxide in boiling 1-propanol for 6 days gave 2,3,4,4a,5,6-hexahydro-l//-pyrido[l,2-a]quinazolin-6-one (343) as a by-product and 3-hydroxy-l-(5-propoxypentyl)-l//-benz(c)-pyrazole (342) [93JCS(P1)1119]. 

An X-ray crystal structural determination revealed that the 8-carboxyl group of cij-4fl,8-H-l,3,4,4a,7,8-hexahydropyrido[l,2-c][l,3]oxazine-8-carboxylic acid is in a pseudoaxial position (81JA7573). The crystal structure of 4-phenyl-2- 4-[4-(2-pyrimidinyl)piperazin-l-yl]butyl -2,3,5,6,7,8-hexahydro-l//-pyrido[l,2-c][l,3]oxazine-l,3-dione was determined by an X-ray investigation (95ZK899). 

Microwave irradiation of 3-(fur-2 -ylmethylene)-l,5-dimethyl-2,6-diphenylpiperidin-4-one 609 with urea/thiourea using neutral alumina gave 4,4a,5,6,7,8-hexahydro-377-pyrido[4,3- pytimidine derivatives 610 and 611, respectively (Equation 52) <2005IJB2527>. 

Ab initio Hartree-Fock and density functional theory (DFT) calculations were performed to study the transition state geometry in intramolecular Diels-Alder cycloaddition of azoalkenes 18 to give 2-substituted 3,4,4a,5,6,7-hexahydro-87/-pyrido[l,2-A]pyridazin-8-ones 19 (Equation 1) <2001JMT(535)165>. 

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