9-Hydroxy-9-phenylperhydropyrido

Irradiation of 4-(3-benzoylpropionyl)-1,4-morpholine (267) yielded an epimeric mixture of 9-hydroxy-9-phenylperhydropyrido[2,l-c][l,4]oxazin-6-ones 268 and 269 via hydrogen abstraction from the position 3 of the morpholine moiety of 267 (98T2529). It was assumed that the steric hinderance between the phenyl group and the hydrogen atoms of 5-methylene group of 267 in the biradicals contributed to the observed selectivity. 

A single stereoisomer of 4-methyl-3-phenylperhydropyrido[2,l-c][l,4]oxa-zine 279, containing a fused bicycle, was obtained by the cyclization of l-(2-hydroxyethyl)-2-piperidinemethanol 235 in CH2CI2 on the action of cone. H2SO4 (97JHC1813). Similarly, l-phenylperhydropyrido[2,l-c][l,4] oxazine 281 was obtained from l-(2-hydroxyethyl)-2-[(phenyl)hydroxy-methyljpiperidine 280. 

Reaction of 40% glioxal with silylated compounds 308 (97SL799, 99SL1094, OOJOC4435) and 310 (97SL799) gave a diastereomeric mixture of l-hydroxy-4-phenylperhydropyrido[2,l-c][l,4]oxazines 309 and 311, respectively. Similarly, diastereomeric mixtures of 8-substituted l-hydroxy-4-phenylperhydropyrido[2,l-c][l,4]oxazines were prepared (01EJOC2385). 

Mild acidic hydrolysis of amino nitrile 369 gave m-4,9a-/7-rra r-9-7/-9-benzyloxy-4-phenyl-3,4,9,9a-tetrahydro-17/,67/-pyrido[2,l-d[l,4]oxazin-l-one <1996TL4001>. (2A)-2-Cyano-l-[(lR)-2-hydroxy-l-phenylethyl]piperidin-6-one, on standing for 20 days in ethanol saturated with HC1 gas, afforded (4/ ,9aA)-4-phenylperhydropyrido[l,2-4[l,4]oxazine-l,6-dione, which was sometimes accompanied by the unstable (26 )-l-[(l/ )-2-hydroxy-l-phenylethyl]-... 

THF at room temperature for 220 min to give 4-phenylperhydropyrido [2,1 -c][1,4Joxazin-6-one (07USA2007/0117839). Reduction of ethyl 1-[1-aryl-2-hydroxyethyl]-6-oxopipeperidine-2-carboxylates with NaBH4 in MeOH at 0 °C for 80-100-min-yielded l-hydroxy-4-arylperhydropyrido [2,1 -c] [ 1,4] oxazin-6-ones. 

Alkoxy-3-phenylperhydropyrido[2,l-c][l,4]oxazines were formed from the 3-hydroxy derivative 25 (R = OH) in boiling alcohols via an intermediate carbenium-oxonium ion, stabilized by the 3-phenyl group [78JMC460 90AP(323)53],... 

---