3- Phenyl-5,6-dihydro-477-1,2-oxazine

Nitroso compounds react with 1,3-dienes to form oxazine derivatives. Aromatic nitroso compounds, Ar—N=0, undergo cycloaddition with most dienes. Thus, butadiene and nitrosobenzene react readily at 0°C to give A-phenyl-3, 6-dihydro-oxazine in high yield (3.29). With unsymmetrical 1,3-dienes, cycloaddition is often highly regioselective. 

Gabriel has demonstrated the instability of 5,6-dihydro-1,3-4/f-oxazines by reacting the hydrobromide of 2-phenyl-5,6-dihydro-l,3-4i -oxazine (55) with water. Ring opening occurs with the formation of 3-aminopropylbenzoate which is rearranged into 3-benzamido-propanol. 

Drefahl and Horhold discussed the mechanism of N 0 acyl migration in A -benzoyl-l,2-diphenyl-3-aminopropanols. The migration does not seem to be possible in the erythro isomer as it would give an intermediate tetrahydro-1,3-oxazine with a bulky phenyl group in axial position. Consequently the erythro isomer is cyclized with inversion to form 2,5,6-triphenyl-5,6-dihydro-l,3-4 -oxazine... 

Dihydro-2/7- 74 and -4//-l,2-oxazines and thiazines 75 are interrelated by prototropy, being enamines and imines, respectively. In the case of oxazines, the imine form 75 is favored, and there are several well established examples of this system, including the parent heterocycle 75 (X = O) [84MI2]. No tautomeric equilibrium between the 2H and 4H forms has been observed under normal conditions in solution or in the solid state. However, the formation of intermediate 2H isomers 77 was proposed both for the conversion of 3-phenyl-5,6-dihydro-4//-l,2-oxazine 76 (R = Ph, r = R = H) into 2-phenylpyrrole(89TL3471) under strong basic conditions and for thermal decomposition of cyclopentene-fused 1,2-oxazine 76... 

Es kann ferner von Phenyl-acetonitril, Cyanessigsaure-athylester und Acrylsaure-nitril ausgegangen werden. lm letzteren Fall wird die Homologisierung durch Michael-Addition eincr C—H-aciden Verbindung an das erhal-tene 4,4,6-Trimethyl-2-vinyl-5,6-dihydro-4H-l,3-oxazin durchgefiihrt1. 

The crystal structures of 4-phenyl-2- 4-[4-(2-pyrimidinyl)piperazin-l-yl]butyl -2,3,5,6,7,8-hexahydro-177-pyrido[l,2-c][l,3]oxazine-l,3-dione <1995ZK899>, 4-cyano-l-phenyl-l-trifluoromethyl-2,3-dihydro-l/7-pyrido[l,2-r-]pyrimidin-... 

Tetrahydropyrido[2,1 -HI 1,4 oxazinc-7,9-dicarboxylate 278 was obtained from the 1,8-dihydro derivative 277 by hydrogenation over a Pd/C catalyst (Equation 51) <1997CAP2188071 >. Catalytic hydrogenation of an epimeric mixture of (4.S, 9a.S )-l -trimcthylsilyloxy-4-phenyl-3,4,6,7-tetrahydro-l//-pyrido[2,1 -HIl,4]oxazine over Raney-Ni afforded perhydro derivatives <2000SC2565>. 

The only salt of this type was prepared by refluxing of tV-methylimidazole with 3-bromomethyl-6,6-dimethyl-4-phenyl-5,6-dihydro-4//-oxazine in toluene for 5h (473). 

Aldehydes, a-phenyl-, from 2-benzy1-4,4,6-trimethyl-5,6-dihydro-1, 3(4H)-oxazine,... 

Sodium, with l-bromo-3-chloro-cyclobutane to give bicyclo [l.l.O]butane, 51, 55 Sodium amalgam, 50, 50, 51 Sodium amide, with 2,4-pentane-dione and diphenyliodonium chloride to give l-phenyl-2, 4-pentanedione, 51, 128 Sodium azide, 50, 107 with mixed carboxylic-carbonic anhydrides, 51, 49 Sodium borohydride, reduction of erythro-3-methanesulfony-loxy-2-butyl cyclobutanecar-boxylate, 51, 12 reduction of 2-(1-phenylcyclo-pentyl)-4,4,6-trimethyl-5,6-dihydro-1,3(4H)-oxazine to 2-(1-phenylcyclopentyl)-4,4, 6-trimethyltetrahydro-l,3-oxazine, 51, 25 Sodium cyanoborohydride, used... 

Bei der Behandlung von N-Phenyl-3.6-dihydro-1.2-oxazin mit Phos-phorsaure erfolgt Hydratation unter Ringspaltung und Orton-Umlage-rung bei Zimmertemperatur und mit 20%iger Saure entsteht N-p-Hydroxyphenyl-4-amino-buten-(2)-ol-(l), bei 60° mit 33%iger Saure cyclisiert dieses wahrend der Reaktion zu N-p-Hydroxyphenyl-A -pyr-rolin 28). 

Analog wird aus dem Addukt mit HCl bzw. HBr N-p-Halogenphenyl-A -pyrrolin gebildet (45). Dagegen fiihrt konzentrierte Schwefelsaure 2-Phenyl-4.5-dimethyl-3.6-dihydro-l,2-oxazin in l-Phenyl-3.4-dimethyl-pyrrol tiber 45)... 

Diese Reaktionsart ist bei den Addukten aus Butadien-carbonsaure-Derivaten mit der Carboxylgmppe in 3-Stellung allein verwirklicht dabei entstehen 3-Amino-a-pyrone [58, 70, 72). So geht das N-p-Chlorphenyl-3-methoxycarbonyl-6-phenyl-3.6-dihydro-1.2-oxazin bei der Chromato-graphie an Aluminiumoxid in 3-p-Chloranilino-6-phenyl-a-pyron uber (55), der Mechanismus ist analog dem der Pyrrolbildung. 

No loss of optical purity was observed in the mild acidic hydrolysis of the enantiomerically pure 6-alkoxy -phenyl-5,6-dihydro-4/7-l,3-oxazine 132, which resulted in formation of (R)-3-benzoylamino-3-phenylpropanal 133 in excellent yield (Scheme 20). Hydrolysis of the analogous tetrahydro-l,3-oxazin-2-one 134 to 133 required a stronger acidic medium and took place only in poor yield, but without any decrease in the optical purity <20000L585, 2003JOC4338, 2004TL9589>. 

Methylene-6-phenyl-2-trichloromethyl-5,6-dihydro-4i/-l,3-oxazine 137 proved applicable as a precursor for a 2-acylamino-l,3-diene as a Diels-Alder cycloaddition partner. Treatment of 137 with DMAD in the presence of Zn(OTf)2 (0.2 equiv) in toluene at 100 °C provided cycloadduct 138 in 57% yield after 2 days (Equation 13) <2006OL3537>. 

Reduction of cycloalkane-condensed 2-phenyl-5,6-dihydro-4//-l,3-benzoxazines 144 with lithium aluminium hydride (LAH) afforded A -benzyl-substituted 2-(aminomethyl)cycloalkanols 145 in a reductive ring opening via the ring-chain tautomeric tetrahydro-l,3-oxazine intermediates. Catalytic reduction of 1,3-oxazines 144 under mild conditions in the presence of palladium-on-carbon catalyst similarly resulted in formation of the A -benzyl-1,3-amino alcohols 145. When the catalytic reduction was performed at elevated temperature at hydrogen pressure of 7.1 MPa, the N-unsubstituted 2-(aminomethyl)cycloalkanols 146 were formed in good yields (Scheme 22) <1998SC2303>. 

Chiral nonracemic bidentate 2-[o-(diphenylphosphino)phenyl]-5,6-dihydro-4//-l,3-oxazine derivatives proved to be effective P,N-ligands in Pd-catalyzed asymmetric transformations. When used in the Pd-catalyzed allylic alkylations of 1,3-diphenylallyl acetate with dimethyl malonate, phosphino-oxazines 147 and 148 and the... 

The ring-opening reactions of l,3-oxazin-6-ones with nucleophiles or electrophiles both result in / -amino acid derivatives. Methanolysis of 2-phenyl-4,5-dihydro-l,3-oxazin-6-one 206 under very mild conditions gave methyl 3-(benzoylamino)propionate 207 (Equation 19) <20030L1575>. 

The asymmetric alcoholytic ring opening of 4-substituted-2-phenyl-4,5-dihydro-l,3-oxazin-6-ones proved to be a efficient method for the preparation of enatiomerically pure /3-amino acid derivatives <2005AGE7466>. Treatment of 2,4-diphenyl-4,5-dihydro-l,3-oxazin-6-one 208 in the presence of the bifunctional chiral thiourea catalyst 211 resulted in formation of an enantiomerically enriched mixture of the unchanged oxazinone (iJ)-208 and allyl (4)-3-benzoyl-amino-3-phenylpropanoate 209. The resolved material (iJ)-208 and the product 209 could easily be separated by a selective hydrolytic procedure that converted oxazinone (iJ)-208 quantitatively into the insoluble iV-benzoyl /3-amino acid 210 (Scheme 37). 

A convenient, one-pot procedure devised for the preparation of 2-phenyl-5,6-dihydro-4//-l,3-oxazine 373 was based on the A -bromosuccinimide oxidation of tetrahydro-l,3-oxazine 372, formed in situ from 3-aminopropanol 371 and benzaldehyde (Scheme 69) <2006S2996>. 

The synthesis of l,3-oxazin-4-ones of type 464 is the first example of the formation of a C-O bond in the course of the Norrish-Yang reaction. Upon treatment with 1-hydroxy-l-phenyl-A -iodanyl mesylate, /3-keto amide 460 was converted to the corresponding a-mesyloxy-/3-keto amide 461 in excellent yield. On ultraviolet (UV) irradiation (A>300nm) of 461, 5-hydrogen transfer to the excited carbonyl group occurred and the diradical 462 thus formed underwent MsOH elimination to enolate diradical 463, cyclization of which resulted in formation of 3-methyl-6-phenyl-3,4-dihydro-277-l,3-oxazin-4-one 464 (Scheme 89) <2001S1258>. 

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