A-Monoalkylation

Miscellaneous Resins. Much less important than the melamine—formaldehyde and urea—formaldehyde resins are the methylo1 carbamates. They are urea derivatives since they are made from urea and an alcohol (R can vary from methyl to a monoalkyl ether of ethylene glycol). 

Reaction of / fZ-amyl alcohol with urea in the presence of sulfuric acid gives a monoalkylated urea (61,62). Monoalkyl ureas are used to prepare uracil derivatives which are useful as herbicides, fungicides, and plant growth regulators (61). 

Partial hydrolysis reactions lead to a monoalkyl phosphite, but complete hydrolysis gives phosphorous acid. The hydrogen atom bound to phosphorus can also be replaced by reaction with sodium, showing that the hydrogen atom has slight acidity. 

Method A. Monoalkylation CF3CONH2 (11.3 g, 0.1 mol) in MeCN (100 ml) is stirred with the alkylating agent (0.05 mol), powdered K2C03 (13.8 g) and TBA-Br (1.61 g, 5 mmol) at 50°C. When the reaction is complete, as shown by GLC analysis, the cooled mixture is filtered and the residue washed with CH2C12 (30 ml). The combined organic solutions are evaporated and the amine isolated by chromatography from silica. 

A-Monoalkylated sulphonamides have been obtained (85-98%) using a polymer-supported catalyst [44]. 

Duolite A-IOID [CL form] is washed with an aqueous solution of the sodium salt of the sulphonamide, obtained by the dissolution of the sulphonamide in aqueous NaOH (0.5 M, 100 ml). The resin is washed repeatedly with H,0, EtOH and MeCOMe and dried over P205 for 12 h. The resin (5 g) is then shaken with the alkylating agent (5 mmol) in EtOH (20 ml) at room temperature. The mixture is filtered and the filtrate evaporated to yield the A-monoalkylated product. 

Method A (monoalkylation) The phosphonate (50 mmol) and the alkylating agent (55 mmol) in CH2Cl2 (200 ml) are added to TBA-Br (16.0 g, 50 mmol) and aqueous NaOH (0.5 M, 100 ml) and the mixture is stirred for 1 h at 45 °C. On completion of the reaction, the organic phase is separated and evaporated. The residue is triturated with Et20 (100 ml) and the dried (MgS04) extract is evaporated to give the monoalkylated product. 

A-Alkyl-2,1,3-benzoselenadiazolium salts react with sodium hydroxide with elimination of selenium to give A-monoalkyl-o-phenylenediamines <89SC1381>. The thiaselenazolines (38a) and the diselenazolines (38b) are attacked by trialkyl phosphites at Se with elimination of selenophosphate and incorporation of phosphorus into the ring (87) in place of selenium (Equation (8)) <80CB2699>. 

Similar methodology to that employed above gave dialkylated dihydropyrido[3,2- ]thiadiazines 207a-c (Scheme 29), while alkylation of the oxidized form 208 gave the A -monoalkyl derivatives 209a-c <1998JME2946>. 

This is a general method of preparing enamines from a secondary aliphatic amine and cyclohexanone or cyclopentanone. Acylation of such enamines is the first step in a general procedure for increasing the chain length of a carboxylic acid by 5 or 6 carbon atoms and of a dicarboxylic acid by 10 or 12 carbon atoms.6 Alkylation of enamines of cyclohexanones by alkyl halides 7 or electrophilic olefins,8 followed by hydrolysis, is a good route to a-monoalkyl cyclohexanones. 

The hydrolysis of a monoalkyl phosphate may also be classed as a dephosphonylation reaction, that is, one involving removal of the O-phosphono [(HO)gP(O)-] group.259... 

The acid-catalyzed hydrolysis of orthoesters is very much faster than that of esters. The second-order rate coefficient for the hydrolysis of ethyl acetate is of the order of 10"4 1-mole-1-sec1 at 25°C, whereas that for the hydrolysis of ethyl orthoacetate103 is of the order of 104 l-mole-1-sec 1, and that for the breakdown of a monoalkyl orthoester must be faster still. If the breakdown of the tetrahedral intermediate is partially rate-determining in acid-catalyzed ester hydrolysis, therefore, its concentration must be very small that is, the equilibrium for its formation must be highly unfavourable. This... 

These compounds (92) are prepared by the reaction of the dibromoethyl material (91) with either the disodium salt (43JCS547) or the di-Grignard reagent (50JCS1917) derived from a monoalkyl- or monoaryl-arsine with best yields reported from the latter route (Scheme 19). 

There are several factors that limit the usefulness of alkylation reactions. First, it may be difficult to limit reaction to monosubstitution because introduction of one alkyl substituent tends to activate the ring towards a second substitution (see Section 22-5). Therefore, to obtain reasonable yields of a monoalkyl-benzene, it usually is necessary to use a large excess of benzene relative to the alkylating agent ... 

Finally, in the most complex multicomponent reaction involving isocyanides, the 7-CC proposed by Ugi in 1993 [93], a moderate diastereoselectivity, leading to a 2 1 mixture of epimeric thiazolidines 109 was observed. The reaction is a combination between an Asinger condensation, involving an a-mercaptoaldehyde (generated from the a-bromoaldehyde and SH ) and an Ugi-type 4-CC with a monoalkyl car-boxylate as acid component (Scheme 1.38). Although the relative configuration of the major stereoisomer was not demonstrated, it is probably trans, in line with the results of Ugi condensation with chiral thiazolines, reported above in Scheme 1.19. 

Reaction of 1,1,1-trifluoroethane with fluorinated ethylenes requires pure antimony pentafluoride as a catalyst. Reaction with TFE gives a monoalkylation product in high yield addition to CH2=CF2 results in formation of a branched alkane 61 [7]... 

Iodination of 2-aminopyridine under a variety of experimental conditions gives, in all cases, 2-amino-5-iodopyridine when only one molar equivalent of iodine is used. Yields range as high as 90%.°7,71,89-94 The A-monoalkyl and A,A-dialkyl derivatives behave similarly.92... 

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