Trimethyl ortho formate

One can also acetalize carbonyl compounds completely without using the alcohol in excess. This is the case when one prepares dimethyl or diethyl acetals from carbonyl compounds with the help of the ortho formic acid esters trimethyl ortho formate HC(OCH3)3 or triethyl ortho formate HC(OC2H5)3, respectively. In order to understand these reactions, one must first clearly understand the mechanism for the hydrolysis of an orthoester to a normal ester (Figure 9.13). ft corresponds nearly step by step to the mechanism of hydrolysis of 0,0-acetals, which was detailed in Figure 9.12. The fact that the individual steps are analogous becomes very clear (see Figure 9.13) when one takes successive looks at... 

When l-dicyanomethylene-3-indanone was treated with trimethyl ortho formate and a substituted aniline in the presence of AcOH it gave anilinomethylene-indanone 99 followed by ring closure and Dimroth rearrangement to indanopyridine 100 (89M781) (Scheme 31). 

The synthesis of chroman 15 involves an acid-catalyzed condensation of trimethyl hydroquinone (14) with methyl vinyl ketone (9), but unfortunately the mechanism is not clarified in detail and the role of the ortho formate is also not clear. Scott et al. assumed that the reaction proceeds via the intermediates 27 and 28. ... 

The method has been applied by the submitters2 to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl ortho-formate of phenylethynyl -butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl tt-orthovalerate and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. w-Butylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190° for 3 hours. 

The major problem of the direct carbonatation of alcohols is of course the formation of water and the unfavorable thermodynamics of the process. Attempts to overcome this problem include the addition of water-trapping agents or start from alcohol derivatives such as ortho esters. A number of such experiments have been carried out under conditions considerably beyond the critical data of pure CO2 [88]. The presence of the supercritical phase as a solvent was explicitly addressed in the synthesis of glycerol carbonate from glycerol and CO2 [89]. The tin-catalyzed conversion of trimethyl ortho ester to dimethyl carbonate in SCCO2 occurred with up to ca. 30 catalytic turnovers, whereby the highest yields and selectivities were observed in the vicinity of the critical pressure of pure CO2 [90]. 

A mixture of DAMN (100 g, 0.925 mol) and trimethyl orthoformate (350 ml, 3.20 mol) is stirred and heated under partial reflux through a 25 cm Vigreux distillation column. Around 200 ml of distillate, mainly methanol and methyl formate, is collected, b.p. 50-70°C, over 140 min. The distillation temperature is allowed to rise to 102°C, and distillate is slowly collected over 2h (the pot temperature is 115°C). The fractionating column is removed, and the bulk of the remaining ortho ester is distilled off. The residue is distilled... 

Carbonyl groups of simple aliphatic aldehydes, ortho mdpara quinones, a,P-unsaturated carbonyls and cyclic aromatic anhydrides are known to condense with trimethyl phosphite, producing phosphite esters [62]. Lebo and Lonsky used trimethyl phosphite to determine the light-induced formation of ort/jo-quinonoid functional groups in refiner mechanical pulp [63]. 

The mononuclear trimethyl complexes RfNPNjTaMej (R = Ph, Cy), 71, have been used for the synthesis of dinuclear tetrahydride complexes [ R(NPN)Ta 2(p-H).j], 72 [225-227]. The tetrahydride complexes exclude dihydrogen to generate coordinatively unsaturated dinuclear dihydride (Ta = Ta) species, 73, that activates ortho-C-H bond of phenyl group of the NPN ligand to generate 74 [228]. Addition of 1 equiv. of hydrazine to 72 results in the clean formation of... 

---