2,4,4,6-Tetramethyl-5,6-dihydro-1,3- oxazine

On the other hand, sublimation of iV-isobutyroylcycloxobuxidine-F, under high vacuum, leads to the ring-opened product (171). A dihydro-oxazine (172) is obtained when sublimation is carried out in the presence of a base (tetramethyl-ammonium hydroxide). 

Tetramethyl-5,6-dihydro-1,3 (4H) -oxazine, for synthesis of substituted acetaldehydes, 51, 30 ... 

This technique may also be modified to prepare acetaldehyde derivatives by use of 2,4,4,6-tetramethyl-5,6-dihydro-l,3(4H)-oxazine1 2 3 4 5 6 7 and 2-carboethoxy acetaldehydes using 2-(carbo-ethoxymethyl)-4,4,6-trimethyl-5,6-dihydro-l,3(4H)-oxazine.3 Functionalized aldehydes and dialdehydes may also be obtained by suitable modification.8 Generally, the intermediates can be used without purification and the overall yields of the aldehydes range from 50-70%. 

The reaction of 2,4,4,6-tetramethyl-5,6-dihydro-4//-l,3-oxazine 139, lithiated at the 2-methyl group, with (—)-(3)-menthyl -toluenesulfmate afforded 2-aryIsulfmylmethyl-1,3-oxazine 142 as a mixture of its diastereomers (Equation 22) <2001 H(55) 1937, 2004T9171>. 

M. Fieser and L. E. Fieser, Reagents for Organic Synthesis, Wiley-Interscience, London, Vol. 3, 1972 Vol. 4, 1974 (article 2,4,4,6-Tetramethyl-5,6-dihydro-l,3-(4//)-oxazine and references cited therein). 

KETONES Lithium diisopropylamide. Nickel carbonyl. Sodium tetiacarbonyl-ferrale(-II). Thallium(IIl) nilrale. 2,4,4,6-Tetramethyl-5,6-dihydro-l,3-(4/0-oxazine. Triphenylmcthyl hexafluorophosphate. y-KETONlTRILES Sodium cyanide. d-LACTONES Silver nitrate. 7-LACTONES a-Chloro-N-cyclohexylpro-panaldoximc. 

The sequence provides an alternative to the aldehyde synthesis of Meyers using 2,4,4,6-tetramethyl-5,6-dihydro-l,3-(4H)-oxazine (3,280-282 this volume) but has the advantage that strongly acidic conditions are not necessary. 

In a new variation for the two-carbon homologation of alkyl halides to give aldehydes,3 2,4,4,6-tetramethyl-5,6-dihydro-l,3-(4H)-oxazine is first converted into the stable, crystalline methiodide salt (5) by treatment with 4.0 eq. of methyl iodide in the dark for 20 hr. The salt (5) is treated with sodium hydride in dry DMF at room temperature. The alkyl halide is then added and the reaction mixture is stirred at 50-55° until... 

ALDEHYDES 1,3-Bis(methy lthio)ally 1-lithium. 2,4-Dimethylthiazole. Ethyl vinyl ether. Methyl methylthiomethyl sulfoxide. 2-Methyl-3-thiazoline. Nickel-aluminum alloy. Sodium tetracarbonylfer-rate(-II). 1,1,3,3-TetramethyIbutyl isocyanide. 2,4,4,6-Tetramethyl-5,6-dihydro-l,3-(4H)-oxazine. Thallium(III) nitrate. 

Stork overcame the dialkylation problem at the a-carbons in aldehydes by using imines. The obvious disadvantages of this method are the unstable starting materials (Schiff bases). Meyers and coworkers found that the stable commercial starting material 2,4,4,6-tetramethyl-5,6-dihydro-l,3-4A/-oxazine 43 can be used as a precursor for formation of various aldehydes. After lithiation of the methyl group in the 2 position it acts as an excellent nucleophile in reaction with various electrophiles E, and after reducing the double bond and hydrolysis the aldehyde group is formed (equation 15). 

Synthesis of carboxylic acids. Dihydro-1,3-oxazines are hydrolyzed by aqueous hydrobromic acid to carboxylic acids.6 This fact, coupled with the fact that this ring system is completely inert to Grignard derivatives, forms the basis for a new synthesis of carboxylic acids.7 Thus 2,4,4,6-tetramethyl-5,6-dihydro-1,3-(4H)-oxazine (1) is alkylated with 1,5-dibromopentane to produce (2). This is converted into the nitrile (3), then the phenyl ketone (4) finally acid hydrolysis gives 7-benzoylheptanoic acid (5). 

CARBOXYLIC ACIDS 2,4,4,6-Tetramethyl-S, 6-dihydro-l, 3-(4H)-oxazine. Tetraethyl dimethylamino-methylenediphosphonate. 2,4,4-Trimethyl-2-oxazoline. 

The C chemical shift values for the tetramethyl-1,2-oxazinium salt (3) and for some 677-1,2-oxazines and dihydro-1,2-oxazines (4)-(8) are given in Table 1. 

The reaction of 1,3,2-dioxarsinane 83 with acetonitrile under acidic conditions produced 2,4,4,6-tetramethyl-5,6-dihydro-477-l,3-oxazine 84 in low yield (30%). The latter then was converted to the amino alcohol 85 by basic hydrolysis (Scheme 26) <2005RCB1543>. 

Related Reagents. Benzothiazole 2-Methyl-2-thiazoline 5, 6-Dihydro-2,4,4,6-tetramethyl-1,3(4/ -oxazine 2,4,4-Trime-... 

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