Dimethoxy ketals, reductive

Reductive Carbonylation of Dimethoxy Ketals and Dimethyl Carbonate. Acetaldehyde is obtained via the reductive carbonylation of dimethyl ketals. Equation 12, and dimethyl carbonate. Equation 13 (15). 

This section deals only with solvents whose reduction products are insoluble in the presence of lithium ions. The list includes open chain ethers such as diethyl ether, dimethoxy ethane, and other polyethers of the glyme family cyclic ethers such as THF, 2Me-THF, and 1,4-dioxane cyclic ketals such as 1,3-dioxolane and 1,3-dioxane, esters such as y-butyrolactone and methyl formate and alkyl carbonates such as PC, EC, DMC, and ethylmethyl carbonate. This list excludes the esters, ethyl and methyl acetates, and diethyl carbonate, whose reduction products are soluble in them (in spite of the presence of Li ions). Solutions of solvents such as acetonitrile and dimethyl formamide are also not included in this section for the same reasons. Figure 6 presents typical steady state voltammo-grams obtained with gold, platinum, and silver electrodes in Li salt solutions in which solvent reduction products are formed and precipitate at potentials above that of lithium metal deposition. These voltammograms are typical of the above-mentioned solvent groups and are characterized by the following features ... 

The synthesis of unnatural (+)-mesembrine (387) through the asymmetric synthesis of methyl (i )-l-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390) by cycloaddition of enantiomerically pure vinyl sulfoxide with dichloroketene has been performed 189) (Scheme 43). Vinyl sulfoxide 388 [prepared by conjugate addition of enantiopure acetylenic sulfoxide with (3,4-dimethoxy)phenylcopper] reacted with trichloroacetyl chloride in the presence of freshly prepared zinc-copper couple in THF at 0°C to produce a mixture of mono- and dichloro lactones 389. Reduction of 389 with zinc in acetic acid followed by cyclization and methylation afforded methyl IR-[(3,4-dimethoxy)phenyl]-4-oxocyclohex-2-enyl acetate (390), treatment of which with methylamine brought about amidation and concomitant intramolecular Michael addition to provide 2-oxo-mesembrine (391). Successively, 391 was transformed to (+)-mesembrine (387) in 79% yield (three steps ketalization of an oxo group, reduction of lactam, and deketali-zation)(/S9). 

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