1.3- 477-Oxazines hydrolysis

Suitably protected chiral tetrahydro-l,4-oxazin-2-ones can be deprotonated at the 3-position and the resulting enolates alkylated to give, after oxazine hydrolysis, a-amino acids. The advantage of the method shown in Scheme 13 using compound 170 to give 163 is that it can be used in the synthesis of a-quaternary amino acids <1999EJ01967>. 

JCS(C)2613) systems, and in many cases the starting materials are available via oxazine intermediates (e.g. 113), or by in situ hydrolysis of a nitrile (74GEP2365302). 

A fluorinated oxazine, prepared fromfluoroacetonitrile and 2 methyl-1,3-pen-tanediol, is alkylated at low temperature The resulting products furnish a fluoro aldehydes after botohydride reduction and hydrolysis [JJ4] (equation 99)... 

The thiono derivatives of tetrahydro-1,3-oxazine became a subject matter of some interest since Kjaer and Jensen discovered that products of enzymatic hydrolysis of Malcolma maritima contain 6-methyl- and 6,6-dimethyl-2-thionotetrahydro-l,3-oxazine (26). The authors proved the identity of these compounds with the products of cyclization of 3-hydroxypropyl-isothiocyanate in an alkaline medium. 

The only known derivative of this class was prepared from ethyl 8-anilinecrotonate, ethyl acetoacetate, and benzaldehyde. In the first instance, a pyrimidine derivative is formed, this is then subjected to partial hydrolysis to form the 3,4-dihydro-l,3-2H-oxazine derivative (42). 

Hydrolysis of 5-nitrotetrahydro-l,3-oxazines (51) to form 3-amino-2-nitropropanol derivatives (52) has been studied most exten-... 

If the acid hydrolysis of 1,3-oxazine derivatives is followed by acting with phenyl-isothiocyanate, thiourea derivatives can be formed. ... 

Benz[l,2-e][l,3]oxazin[3,4-a]azepin-6-one (15) is cleaved rapidly in cold ethereal ethylamine to /V.A-diethyl-2-(2-hydroxyphcnyl)-l//-azepinc-1-carboxamide (90% mp 121 -122°C), whereas acidic hydrolysis yields the intramolecularly hydrogen bonded 2-(2-hydro-xyphenyl)-3//-azepine (16).156... 

The conformationally locked racemic enamine, 4-(4-rOT-butyl-1-cyclohexenyl)morpholine, reacts with (l-nitroethenyl)benzene to give a mixture of diastereomeric 1,2-oxazine 2-oxides 1 and 2 (ratio 1/2 75 25). Whether these arise via an ionic or a cycloaddition mechanism is unclear. Hydrolysis of 1 and 2 with dilute acid gave a 80 20 mixture of trans- and cis-ketones, 3 and 414. 

Alkylation and hydrolysis of imines alkylation of aldehydes 10-107 Alkylation and hydrolysis of dithianes 10-108 Alkylation and hydrolysis of oxazines and similar compounds 10-109 Reaction of diazo aldehydes with boranes... 

Alkylation and hydrolysis of dithianes and similar compounds 10-108 Alkylation and hydrolysis of oxazines... 

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]-... 

Tetrahydropyrrolo[l,4]oxazine 74, obtained by photoinduced electron-transfer (PET) oxidative activation of substituted prolinol, undergoes nucleophilic substitution of the OH at position C-3 with allyltrimethylsilane in the presence of TiCU (Scheme 8). The reaction was highly stereoselective and produced, after hydrolysis of the resultant amide 75, optically active a-hydroxy acid 76 together with the auxiliary (.S )-prolinol that can be effectively recycled <1998TL7153>. 

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