5,6-Dihydro-4H-l,3-oxazines

Die Reduktion der 5,6-Dihydro-4H-l, 3-oxazine wird dazu ausgenutzt, um auf einfache Weise aus Acetonitrilen nach Alkylierung Aldehyde zu erhalten ... 

Trimethyl-2-alkyl-5,6-dihydro-4H-l,3-oxazin In einemmitGummi-Kappe und magneti-schem Ruhrwcrk versehenen Riihrkolben werden unter Stickstoff 100 ml abs. THF und 14,1 g (0.1 Mol)... 

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. 

Trimethyl-2-cyclopentylmethyl-tetrahydro-aus 4,4,6-Trimethyl-2-cyclopentylmethyl-5,6-dihydro-4H-l,3-oxazin und Natriumboranat 349... 

Cationic polymerization of unsubstituted 4-membered cyclic amine proceeds in a way similar to that of aziridine, giving branched polymer containing, according to H NMR, 20% of primary, 60% of secondary, and 20% of tertiary amino groups [174]. Purely linear polymer can be obtained by polymerization of 5,6-dihydro-4H-l,3-oxazine, followed by hydrolysis [175] ... 

Als Ausgangsverbindung dienen 2-substituierte 4,4,6-Trimethyl-5,6-dihydro-4H- l,3-oxazine H2 ... 

Alkyl-l, 3-oxazinane Zu einer Mischung von 100 m/ THF und 100 m/ Ethanol (95%ig) in einem 600-m/-Becherglas gibt man 0,1 mol 2-Alkyl-4,4,6-trimethyl-5,6-dihydro-4H-l,3-oxazin (auch als Rohprodukt aus... 

Auf diese Weise erhalt man u.a. (Ausbeute einschl. Alkylierung des 2-Organo-4,4,6-tri-methyl-5,6-dihydro-4H-l,3-oxazins)... 

A number of cyclic monomers containing the imino ether linkage N = C(R)—O— have been successfully polymerized by the ring-opening mechanism. Particularly the derivatives of 2-oxazoline (OXL) u and 5,6-dihydro-4H-l,3-oxazine (OXZ) ° but also 2-iminotetrahydrofuran (ITH)2) and ethylene iminocarbonate (EIC)3> have been studied ... 

In gleicher Weise wie 4,5-Dihydro-l,3-oxa/.ole (s.S. 362) lassen sich Chlormethyl-5,6-dihydro-4H-l,3-oxazine zur Herstellung von Carbonsauren heranziehen643 644 z.B. als Vorstufen zur Herstellung von Aryl-essigsauren645 oder a,/ -ungesattigten Carbonsauren646 ... 

Dihydro-l,3-oxazole bzw. 5,6-Dihydro-4H-l,3-oxazine als cyclische Carbonsaure-ester-imide werden getrennt besprochen (s.S. 819, 823). 

Auch aus 4-Hydroxy- 1-alkenen werden nach einem modiflzierten Tillmann-Ritter-Verfahren80-81 5,6-Dihydro-4H-l,3-oxazine erhalten ... 

Auf analoge Weise erhaltman u.a. 2-Methyl-6-propyl- (56%) bzw. 6-Methyl-2-phenyl-5.6-dihydro-4H-l,3-oxazin (50%). 

Acetonitrile added dropwise with stirring at 3-8 to 92%-H.2SO y then 3-methyl-3-buten-l-oI added slowly at 8-10°, and stirred ca. 25 min. while allowed to warm to room temp. 2,4,4-trimethyl-5,6-dihydro-4H-l,3-oxazine. Y 48%. F. e. s. S. P. McManus and J. T. Carroll, Org. Prep. Procedures 2, 71 (1970) from nitriles, ethylene derivs., and formaldehyde cf. C. Giordano, G. Ribaldone, and G. Borsotti, Synthesis 1971, 92. 

Methyl ester of serine rac-1 under treatment with (diacetoxyiodo) benzene (BAIB) and iodine gives radical 2, which is oxidized to give acyliminium ion 3. This intermediate is then trapped with acetate to yield N,0-acetal 4. The acyliminium ion 3 can regenerate from the acetal and react with vinyl arenes to produce the intermediate 5. In the final step, an intramolecular cyclization furnishes the 6-aryl-5,6-dihydro-4H-l,3-oxazine 6, with the ds isomer rac-6a as the major product (Scheme 5.3) [8]. In a similar domino process, aminosugars provide substituted oxazines, which are analogs of C-nudeosides [8]. 

Sodium tetrahydridoborate hydrogen chloride Aldehydes from 5,6-dihydro-4H-l,3-oxazines s. 23, 56 s. a. J. Org. Chem. 38, 36 (1973)... 

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