Orthocarboxylic —

A more useful method for the synthesis of 1,2,4-tiiazine 4-oxides is the cyclization of a-hydrazonooximes 141 with orthocarboxylates or iminoesters. A variety of 1,2,4-triazine 4-oxides 55 were obtained by this methodology (71 LA 12, 73TL1429, 77LA1713, 78JMC623, 86JHC721, 87KGS257). 

Heteroannelated 1,2,4-triazine 4-oxides—fervenulin 4-oxides 12—were obtained starting from 6-hydrazino-l,3-dimethyl-5-nitrosouracil. Orthocarboxylates, formic acid, dimethyl sulfate, or DMF in the presence of POCI3 were used as cyclization agents (77H273, 78JOC175, 78JOC469). 

Cl Atom as Part of an Acetal- and Orthocarboxylic or Orthocarbonic Acid Function ... 

Crotchet, R. A. Blanton, C. D. TV-Monoalkylation of Primary Aromatic and Heteroaromatic Amines with Trialkyl Orthocarboxylates and Sodium Boro-hydride, Synthesis 1974, 55. 

Many of the methods discussed in this section can also be treated as combinations of more than two fragments. For instance, in the cyclization of a-hydrazono oximes with orthocarboxylates described in the next section, the a-hydrazono oximes (635) are treated as a five-atom fragment, but since these compounds are usually prepared from ketones by nitrosation and reaction of the oximino ketones with hydrazine, the entire reaction sequence may be described asa[2 + l+ 2+ l] combination. 

The cyclization of a-hydrazono oximes (635) with orthocarboxylates is an excellent way of preparing 1,2,4-triazine 4-oxides (636) (73TL1429,7lLA(750)12,77LA1713). Using aldehydes or ketones instead of orthoesters provides 2,3-dihydro derivatives (637 Scheme 22) (75S794). Cyclization of a-hydrazonocarboxamides (638) with carbonic acid derivatives such as ethyl chloroformate affords l,2,4-triazine-3,5-diones (639) (68M1808). The a-hydrazonocarboxamides (638) can be prepared by the reaction of diazonium salts with a-activated acetamides such as cyanoacetamide as shown. 

Aminohydrazines (640) are useful intermediates for the synthesis of reduced 1,2,4-triazines. With nitriles, carboxylic acids, imidates, thioimidates or orthocarboxylates, they form l,4,5,6-tetrahydro-l,2,4-triazines (641) (78HC(33)189, p. 629), with carbon disulfide they give the 3-thiones (642) <78HC(33)189, p.648), and with aldehydes or ketones hexahydro-1,2,4-triazines (643) are formed <78HC(33)189, p. 657). 

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 ... 

Orthocarboxylic Acid Derivatives. Simchen, G. In Carboxylic Adds and Carboxylic Acid Derivatives Falbe, J., Ed, Houbett-Weyl, 4th ed., Vol. E5 Thie-me Stuttgart, 1985 pp 3-192. 

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... 

The first step of the Provost reaction is the reaction of the alkene with iodine to form the cyclic iodonium ion. Next, the iodonium ion is stereospecifically opened by the silver carboxylate to form the corresponding frans-1,2-iodo carboxylate. The iodine is displaced intramolecularly by the carbonyl group of the carboxylate (anchimeric assistance) to form a cyclic cationic intermediate. In the absence of water, this cation is opened with the inversion of configuration by the second equivalent of silver carboxylate to afford the frans-1,2-dicarboxylate. However, in the presence of water Woodward-Brutcher modification) the common intermediate is converted to a c/s-orthocarboxylate which is hydrolyzed to the corresponding c/s-1,2-diol. 

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. 

Table III. Effect of 1-Substituent on the Topical Toxicity to Houseflies of 4-Isopropyl-, 4-t-Butyl- and 4-Cyclohexyl-bicyclo-orthocarboxylate s...

Bicyclic orthocarboxylates are compounds of a group with a structure analogous to BPEs. The structural difference lies in the replacement of the phosphorus moiety of BPEs by a carbon moiety. 

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