Hydro-methyl-addition

The methanol-methyl acrylate azeotrope contains about 45% methyl acrylate, which can be recovered by washing out the methanol with a large volume of water or brine the acrylate is purified by, drying and distilling. An inhibitor, such as hydro-quinone, should always be added to any acrylic ester before attempting to distil it, and, unless it is stored in a refrigerator, the distilled ester should not be kept more than a few hours without the addition of a small amount (0.1-1.0%) of an inhibitor. 

With cyanide ion in aqueous ethanol azepinedicarboxylate 3 forms the corresponding racemic 4,5-dihydro-l//-azepine-4-carbonitrile (85%),121,241 whereas with dimethyl 2,5,7-trimethyl-4//-azepinc-3,6-dicarboxylate (6) diastereospecific addition occurs to give racemic lrans-5-me thy 1-4.5-di hydro-1-//-azepine-4-carbonitrile 7 together with a small amount of the trans 4S-methoxy-5 / -methyl compound 8.121... 

Trimethylsilyl halides can also be used for analogous reactions with arenediazo-nium tetrafluoroborates, as shown by Keumi et al. (1989). These authors treated 2-fluorenediazonium tetrafluoroborate in A/,Af-dimethylformamide or -acetamide with trimethylsilylchloride, -bromide, or -iodide in the presence of an excess of N-chlorosuccinimide, Af-bromosuccinimide, or methyl iodide, respectively, at 60 °C (Cl, Br) or at room temperature (I). The yields of the 2-halofluorenes were good in addition fluorene, the product of hydro-de-diazoniation, was obtained, if the reaction was run in tetrahydrofuran/Af,7V-dimethylformamide mixtures. The mechanism of these reactions, as well as that of the corresponding azido-de-diazoniation, is uncertain (see also Secs. 10.2 and 10.7). 

The addition of oxygen, sulphur, or selenium to 2-hydro-4-methyl-l,3,2-dioxa-phosphorinan proceeds stereospecifically.143... 

In addition, differences between the u.v. spectra of the 6-methyl isomers and the non-methylated analogues were attributed to these steric interactions. Catalytic hydrogenation of trans-cholecalciferol gave mainly the previously unknown (10i )-epimer of dihydrotachysterols (278) whereas hydro-boration-acetic acid treatment gave a 1 1 mixture of (278) and the (105)-... 

Tri-tert-butyl-X -phosphorin24 readily reacts with bromine and with chlorine. Mach oxidizing with bromine in CCI4, could not isolate a crystalline product. The brown colour of the addition product of one mole Br2 to one mole 24 disappeared with water and the crystalline 2-hydro-phosphinic acid 85b could be isolated in 45% yield. Methyl-magnesium-iodide or red phosphorus yielded 2.4.6 tri-tert-butyl-X -phosphorin 24. It seems reasonable to suppose that on bromination l.l-dibromo-2.4.6-tri-tert-butyl-X -phosphorin was formed. 

The BBrs reaction with 1. l-dimethoxy-2.4.6-di-tert-butyl-4-(4 -methoxyphenyl)-X -phosphorin 200 leads to cleavage of both methoxy groups in addition to the methoxy group at the phosphorus, the 4 -methoxy group is attacked. The 2-hydro-4-(4 -hydroxyphenyl)-phosphinic acid methyl ester 201 can be methylated with methyl iodide in methanol/sodium methylate at the phenolic group, leading to 202, which can also be prepared by hydrogen peroxide oxidation of 2.6-di-tert-butyl-4-(4 -methoxy phenyl)-X -phosphorin 204 to 203, followed by diazomethane methylation (see Table 13, p. 61). 

With aromatic and heteroaromatic aldehydes,193 4-oxo-6,7,8,9-tetra-hydro-4T/-pyrido[l,2-a]pyrimidines yielded the 9-arylmethylene derivatives,133,266 whereas with glyoxylic acid the 9-carboxymethylene derivative was formed.266,267 The primary addition product (237) could be isolated from the reaction mixture of ethyl 6-methyl-4-oxo-6,7,8,9-tetrahydro-4//-pyrido[l,2-a]pyrimidine-3-carboxylate and benzaldehyde. On dehydration the addition product (237) gave the 9-benzylidene compound.266 The 9-carboxymethylene derivatives may be transformed by catalytic hydrogenation to the 9-acetic acids, which can be esterified.266,267... 

Oxidative cyclization of unsaturated /3-dicarbonyl compounds with two a-hydro-gen atoms will give products that still have one a-hydrogen and can be oxidized further. If the product is oxidized at a rate competitive with that of the starting material, mixtures of products will be obtained. For instance, oxidative cyclization of 26 affords 36 % of 27 and 10 % of dienone 28 formed by further oxidation of 27, as shown in Scheme 6 [7]. The product is occasionally oxidized much more readily than the starting material so that none of the initial product is isolated. These reactions may still be synthetically useful if the products of further oxidation are monomeric. For example, oxidative cyclization of methyl 3-oxo-6-heptenoate provides 78% of methyl salicylate [29]. The overall reaction consumes 4equiv. Mn(OAc)3. Competitive oxidation of the product is not usually a problem in inter-molecular addition reactions, because a vast excess of the oxidizable substrate, for example acetone or acetic acid, is usually used as solvent. Use of excess substrate is not possible in oxidative cyclizations. 

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