Orthocarboxylic esters

When an orthocarboxylic ester is heated with a primary alcohol, or less well with a secondary alcohol, the alkoxyl groups are exchanged ( trans-esterification ) 871, 872... 

Dihalo ethers also give orthocarboxylic esters readily, by reaction with alkali alkoxides 890 e.g., mixed esters of orthoformic acid are formed on treatment of dichloromethyl methyl ether with various alkoxides,891 and esters of orthooxalic acid are obtained by heating l,l,2,2-tetrachloro-l,2-diethoxyethanes with sodium alkoxides in an autoclave 892... 

Alcoholysis of carbimidic ester hydrochlorides leads to orthocarboxylic esters.15, 895 It is essential to use well-dried alcohols and acid-free imidic ester hydrochlorides and completely to exclude moisture. 

As dehydrating agents, triflic anhydride/Ph3P=0 [408] or [Q-S0-0-CH=N (CH3)2] cr [409] can also be applied. Orthocarboxylic esters R-CH(OEt)3 have been utilized very efficiently with catalysis of ZrOCl2.8 H2O [410]. 

M. Asaoka, N. Sugimura, H. Takei, The reactions of 2-(trimethylsiloxy)furans with orthocarboxylic esters, acetals, and acylal in the presence of Lewis acids. Bull. Chem. Soc. Jpn. 52 (1979) 1953-1956. 

Orthocarboxylates (353) when heated with hydrazines are said to afford dihydro-1,2,4,5-tetrazines (104) (66M1195, 64JMC814, 03JPR(68)464). The first step of the reaction should be the formation of the hydrazidic ester (354). The thermal cyclization of aliphatic hydrazides ... 

Although the orthocarboxylic acids, R—C(OH)3, are unstable, many of their derivatives are known, stable compounds. The known carbohydrate orthoesters are all derived from the structure that results when two of the three hydroxyl groups of an orthoacid are involved in ester formation with two hydroxyl groups of the sugar molecule. General formula A represents those types which are of particular interest in the field of carbohydrates. The two adjacent carbon atoms of the five-membered ring constitute carbon atoms number 1 and 2 of an aldose and either 1 and 2, or 2 and 3 of a ketose. In certain instances it has been... 

Nesterov, L.V., and Aleksandrova, N.A., The Arbuzov reaction for dialkyl(trialkylsilyl)phosphites with esters of orthocarboxylic acids. A new heterolytic chain process in the chemistry of organophosphorus compounds, Zh. Obshch. Khim., 55, 222, 1985 J. Gen. Chem. USSR (Engl. Transl.), 55, 195, 1985. 

Dihydrotetrazines (340), which can easily be oxidized to 1,2,4,5-tetrazines, can be formed by dimerization of thiohydrazides (337) or amidrazones (338). The ring closure of hydrazidines (339) in a [5 + 1] fashion proceeds well with activated carboxylic acid derivatives such as imidates (341), orthocarboxylates (342) or dithiocarboxylates (343). The [4 + 2] procedure is found in the transformation of 1,3,4-oxadiazoles (346) or 1,4-dichloroazines (345) with hydrazine. Finally diazoalkanes (344) can be dimerized in a [3 - - 3] manner under the influence of a base the dimerization of diazoacetic ester is an early example, leading to 3,6-tetrazinedicarboxylate (48), which is frequently used in (4 -I- 2) cycloaddition reactions with inverse electron demand. Nitrile imines, reactive intermediates which are formed from many precursors, can dimerize in a [3 -I- 3] fashion to form 1,3,4,6-tetrasubstituted 1,4-dihydrotetrazines. These reactions are summarized in Scheme 57. 

A soln. of guanylurea in abs. methanol treated with dimethylformamide dimethyl acetal, and allowed to stand overnight at room temp, under anhydrous conditions -> 5-azacytosine. Y 91%. Also with ethyl orthoformate in dimethylformamide and f. e. with orthocarboxylic acid esters s. A. Piskala, Coll. 32, 3966 (1967). 

Orthocarboxylic acid esters from 1,1,1-trihalides CHalg C(OR)3... 

Orthocarboxylic — s. a. Thio-orthocarboxylic acid esters -----, cyclic... 

Cyclic orthocarboxylic acid esters from lactones... 

Esterification under mild conditions can be performed with 0-alkyl-N,N-dicyclohexylisoureas A new transesterification technique has been reported which uses molecular sieves to shift the equilibrium by selective absorption of the resulting alcohol A simple, one-stage process for the monodecarbalkoxyla-tion of malonic esters, by sodium cyanide, has been published . Orthocarboxylic acid derivatives of carbohydrates have been used for the stereospecific preparation of l,2-fran5-glycosides... 

Carboxylic from orthocarboxylic acid esters C(OR)g -> COOR... 

Glycol esters from cyclic orthocarboxylic acid esters C... 

Carbohydrate orthocarboxylic acid esters from glycosyl dihalides... 

Urethans from orthocarboxylic acid esters NH - NCOOR... 

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