[1850-14-2] · C5H12O4 · Tetramethyl Orthocarbonate · (MW 136.17)
(CO2 fixation; formation of orthocarbonates from diols; electrophilic introduction of an ester functionality)
Alternate Names: tetramethoxymethane; methyl orthocarbonate.
Physical Data: mp -5.5 °C; bp 114 °C; nD 1.3864; d 1.023 g cm-3.
Form Supplied in: colorless liquid; widely available.
Preparative Methods: has been prepared by heating a solution of Sodium Methoxide in methanol with chloropicrin,1 Trichloroacetonitrile,2 or thiocarbonyl perchlorate;1 the best yields have been obtained with the perchlorate. Alternatively, disodium hexamethoxystannate (prepared in situ from sodium methoxide and tetrachlorostannane) can be refluxed with Carbon Disulfide in methanol to form the orthocarbonate.3
Handling, Storage, and Precautions: flammable; moisture sensitive.
Replacement of one of the methoxy groups of tetramethyl orthocarbonate with a cyano group can be efficiently accomplished by treatment with Cyanotrimethylsilane in the presence of a Lewis acid such as Iron(III) Chloride,4 Tin(II) Chloride,5 or Tin(IV) Chloride (eq 1).6
The title reagent has been employed in the
fixation reaction of CO2 with diethylamine, providing excellent yields of the methyl carbamate (eq 2).7
Tetramethyl orthocarbonate can be used to protect ribonucleosides as their 2´,3´-orthocarbonates, which are stable to basic conditions. The orthocarbonate may also be transformed, under aqueous acidic conditions, into an acid-stable cyclic carbonate protecting group (eq 3).8
The acid-catalyzed reaction of tetramethyl orthocarbonate with 2 equiv of a diol at 110 °C affords symmetrical spiroorthocarbonates. Their unsymmetrical counterparts can be prepared via a two-step procedure (eq 4).9
Conversion of 2-mercaptoalcohols to thiiranes can be accomplished with tetramethyl orthocarbonate in the presence of p-Toluenesulfonic Acid (eq 5).10
Tetramethyl orthocarbonate can be used as an electrophile to introduce an ester functionality (eq 6).11
Mary Ann M. Fuhry
University of Cambridge, UK