Orthocarbonic acids derivatives

From guanidinium salts or orthocarbonic acid derivatives... 

This is presumably the only example of an orthocarbonic acid derivative formed by addition of CO2 to the oxime groups. Unfortunately the electronic structure of [Ni(L1833)] has not yet been studied. According to X-ray diffraction results nickel has the formal oxidation state of zero. 

From orthocarbonic acid derivatives 2.72.4.9 Miscellaneous methods... 

Orthocarbonate. A derivative of the hypothetical orthocarbonic acid, as ethyl orthocarbonate, C(OC2H6)4. The common inorganic carbonates are metacarbonates, derived from metacarbonic acid, H2C03. 

Practically all methods which have been proposed for the preparation of guanidine salts involve either ammonation or ammonolysis of some derivative of carbonic acid. Phosgene,1 chloropicrin,2 and esters of orthocarbonic acid2 react with aqueous ammonia to give small yields of guanidine. The hydrochloride is obtained when carbon tetrachloride3 is acted upon by liquid ammonia under pressure. Urea4 is partially ammonolyzed in the presence of ammonium chloride. 

This reaction is thermodynamically controlled, because the polymer containing 1,3-dioxolane rings converts itself to a polyether when allowed to stand at room temperature for several days or heated at 80 °C for a few hours in the presence of an acid catalyst. Similar double ring-opening polymerizations were observed for 2,6,7-trioxabicyclo[2.2.2]octane and its derivatives [86, 87] and for spiro orthoesters and spiro orthocarbonates as well (see Sects. 6 and 7). 

Unlike the model system, (66) could not be brominated directly. Therefore, it was converted into the ketone (67) by heating in 80% acetic acid, and this ketone was brominated with excess bromine in ether to give (68). Conversion of (68) into the acetal (69) was accomplished with diethylene orthocarbonate and toluene-p-sulphonic acid. Rearrangement of (69) to (70) was effected by heating with excess 1,5-diazabicyclo[3,4,0]nonene in xylene-DMSO. On comparison of i.r., n.m.r., and mass spectral data, this synthetic racemate was identical with the corresponding derivative from natural chasmanine. 

Ribonucleoside 2 J -orthocarbonates. Under acid catalysis (p-toluenesulfonic acid) ribonucleosides (1) undergo exchange with tetramethyl orthocarbonate (excess) in anhydrous dioxane solution to give 2, 3 -0-dimethoxymethylidene derivatives (2) in 50-80% yield. The derivatives are converted by mild acid treatment (98% formic acid) into 2, 3 -carbonates (3). The sequence may have useful... 

The derivatives of anthranilic acid 179 (the products from the condensation of primary amines and the respective isatoic anhydrides) were treated with orthocarbonic ester, and the obtained compounds 180 were cyclized to the derivatives of 2,4-quinazolinedione 181 by the action of an alcohol solution of potassium hydroxide [67, 96, 104, 105],... 

The dimethoxymethylene group is potentially useful for the protection of glycol systems. Ribonucleosides undergo acid-catalyzed exchange with tetramethyl orthocarbonate to give 2 3 -0-dimethoxymethylene derivatives [176]. Such cyclic orthocarbonates are stable in alkaline media, but are converted into the corresponding 2, 3 -cyclic carbonates under mild conditions of acidic hydrolysis [176]. Thus the half-time of hydrolysis of 2 3 -0-dimethoxymethyleneadenosine (101) is 10 min [176] in O.OlTV-hydrochloric acid at 20°. 

The free ortho acids have not been isolated because of their thermodynamic instability, and early attempts aimed at their detection were not successful [1]. However, the ortho esters are stable derivatives which have the general structure I. Related to the ortho esters are derivatives in which the R, R", R" = —OR, —OH, —COR. The thio ortho esters have sulfur in place of oxygen in the structures above. The orthocarbonates ROC(OR) and C(0R)4 can also be considered ortho esters. 

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