Dimethyl carbonate preparation from carbon dioxide

In 1970, it was disclosed that it is possible to achieve the conversion of dimethylformamide cyclic acetals, prepared in one step from vicinal diols, into alkenes through thermolysis in the presence of acetic anhydride." In the context of 31, this two-step process performs admirably and furnishes the desired trans alkene 33 in an overall yield of 40 % from 29. In the event, when diol 31 is heated in the presence of V, V-dimethylforrnamide dimethyl acetal, cyclic dimethylformamide acetal 32 forms. When this substance is heated further in the presence of acetic anhydride, an elimination reaction takes place to give trans olefin 33. Although the mechanism for the elimination step was not established, it was demonstrated in the original report that acetic acid, yV, V-dimethylacetamide, and carbon dioxide are produced in addition to the alkene product."... 

The 1,2,6-thiadiazines 571 are prepared from the -diketones 569 and sulfamide 570 in high yields (Scheme 257) <1965M216>. An efficient synthesis of iV-aryl-l,2,6-thiadiazine 1,1-dioxides 573 is based on the cyclization of 3-chloropropyl phenylsulfamide 572 using potassium carbonate in dimethyl sulfoxide (Scheme 258) <2003TL5483, 2003T6051, CHEC-III(9.07.9)385>. 

Direct introduction of the carboxyl group into an aromatic ring is accomplished with urea hydrochloride, phosgene, oxalyl chloride, or carbon dioxide. Carboxylation of benzene is effected in 15-58% yields by treating with liquid phosgene and aluminum chloride. No catalyst is required in the conversion of dimethylaniline and phosgene to p-dimethyl-aminobenzoic acid (50%). 9-Anthroic acid (67%) is prepared from anthracene by heating to 240° with oxalyl chloride and nitrobenzene. ... 

The first lithiopyrazine derivative was prepared by Hirschberg et al. (1015) from 3-iodo-2,5-dimethylpyrazine and butyllithium in ether subsequent reaction with (a) carbon dioxide gave 3-carboxy-2,5-dimethylpyrazine, and (b) several aromatic aldehydes gave the carbinols (62, R = H, p-methoxy, m-nitro) (1015). Similar reactions were observed when 2-formylpyridine and 2-acetylpyridine (1016) were used as the carbonyl compounds, but with acetaldehyde attempted reactions were unsuccessful (1015). A patent also describes the preparation of many carbinols from 2,5-disubstituted 3-iodopyrazines (164). The lithio reagent derived from 3-iodo-2,5-dimethylpyrazine (with butyllithium in hexane) with 2-nitrobenzaldehyde gave 2,5-dimethyl-3[ 1 -hydroxy-1 (2"-nitrophenyl)methyl] pyrazine (1017). 

A fourth type of product, a carbamate RNHCOOR , can be obtained from primary or secondary amines, if these are treated with CO, O2, and an alcohol R OH in the presence of a catalyst. " Primary amines react with dimethyl carbonate in supercritical CO2 (see p. 414) to give a carbamate. " Carbamates can also be obtained from nitroso compounds, by treatment with CO, R OH, Pd(OAc)2, and Cu(OAc)2, " and from nitro compounds. " When allylic amines (R2C=CHRCHRNR 2) are treated with CO and a palladium-phosphine catalyst, the CO inserts to produce the p,y-unsa-turated amides (R2C=CHRCHRCONR 2) in good yields. " Ring-expanded lactams are obtained from cyclic amines via a similar reaction (see also, 16-22). Silyloxy carbamates (RNHC02SiR 3) can be prepared by the reaction of a primary amine with carbon dioxide and triethylamine, followed by reaction with triisopropylsilyl triflate and tetrabutylammonium fluoride. ... 

Carboxylic acids could be prepared from compounds containing an active hydrogen atom with dry carbon dioxide in the presence of 2-12 mol equiv. of DBU at ambient temperature in dimethylformamide or dimethyl sulfoxide, or without solvent (74CL427 77JAP(K)202). The yields of the carboxylic acids increased with the pressure of carbon dioxide (77JAP(K)202). 

Reaction of l-chloro-4,4-bis(chloromethyl)pentane with magnesium in diethyl ether, followed by quenching with carbon dioxide, gave 4-(l-methylcyclopropyl)butanoic acid in 68% yield. Cyclopropane derivatives with electron-withdrawing substituents 5 were prepared by elec-troreductive dechlorination of 2,4-dichlorobutanoic acid derivatives in dimethyl sulfoxide solution in the presence of tetraethylammonium 4-toluenesulfonate at ambient temperature (yields 51 -90%).The starting materials for compounds 5 can easily be obtained by copper (I)-catalyzed photochemical addition of dichloromethane to electron-deficient alkenes. Electrochemical reductive 1,3-debromination has also been achieved however, it is of little synthetic value (experimental details are described in ref 16, with yields ranging from 39 to 94%). meso- and dimethyl sulfoxide gave equal amounts of cis- and transA, 2-dimethylpropane. ... 

Carbonates and carbamates. In the presence of phosphine-CBr4 and base, alcohols combine with CO2 to afford carbonates. Mixed carbonates are obtained under different conditions, and with a Mg—A1 mixed oxide as catalyst, epoxides formed cyclic carbonates. The preparation of dimethyl carbonate from acetone dimethyl acetal and supercritical carbon dioxide in the presence of a metal catalyst (e.g., dibutyltin methoxide) is successfully carried out. ... 

Dimethyl carbonate. A direct preparation from methanol and carbon dioxide in the presence of BuaSnfOBu) is possible at elevated temperature and pressure. The addition of a water scavenger such as DCC increases the yield. 

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