Dimethyl dicarbonate reactions

The acylpalladium 141 is formed by oxidative addition of acid anhydride to Pd(0), and can be used for synthetic purposes [61]. The mixed anhydride 143 was prepared in situ by the reaction of benzoic acid with dimethyl dicarbonate (142), and the benzoylpalladium methoxide 144 is generated by decarboxylative oxidative addition of 143, and is used for Suzuki coupling with arylboronic acid to yield the diaryl ketone 145 [62]. 

Diethyl dicarbonate (diethyl pyrocarbonate) was used in the past as a preservative for soft drinks and some alcohohc beverages (including wine). In aqueous solution, however, diethyl dicarbonate is rapidly hydrolysed to ethanol and carbon dioxide, and in alcoholic beverages it is transformed into diethyl carbonate by reaction with ethanol. In the presence of ammonium salts toxic ethyl carbamate then results, which is also known as urethane (Figure 11.2). For these reasons, diethyl dicarbonate is not approved in the EU, but the approved compound is dimethyl dicarbonate (E242), which can be used for the preservation of soft drinks, teas, herbal teas and in some countries to stabilise wine. The methyl carbamate produced from dimethtyl dicarbonate is a non-toxic substance. In treated wines it occurs in amounts up to 10 xg/l. 

The functionalized allene, DIMETHYL 2,3-PENTADIENEDIOATE, the first in the series, is an intriguing substrate for various addition and cycloaddition reactions. Finally, a new reagent, DI-ferf-BUTYL DICARBONATE, for he formation of A-f-BOC derivatives which eliminates the use o the hazardous fert-BUTYL AZIDOFORMATE (WARNING) is intrqduced. 

Z)-2-butenylene dicarbonate with dimethyl malonate gives a low yield (20—40%) of 2-vinylcyclopropane-l,l-dicarboxylate with up to 70% ee (Scheme 2-38) [54], Reaction with methyl acetoacetate or acetylacetone takes place in a different manner to give a dihydrofuran derivative (59% ee), which results from nucleophilic attack of enolate oxygen at the cyclization step, (c) Asymmetric elimination of an acetyl-acetate ester gives (R)-4-rerr-butyl-l-vinylcyclohexene of up to 44% ee (Scheme 2-39) [55]. (d) Palladium-catalyzed allylic silylation is also applied to asymmetric synthesis... 

Various alkylcyclopropanes have been converted to (l-alkenyl)cyclopropanes by dehydrogenation with trimethylsilyl triflate, selenium dioxide,tetrachloro-1,4-benzoquinone, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, di-/er/-butyl dicarbonate and potassium tert-butoxide/dimethyl sulfoxide. A related transformation is the Ramberg-Back-lund reaction of bis(l-trimethylsilylcyclopropylmethyl) sulfone which gave ( )-l,2-bis(l-trimethylsilylcyclopropyl)ethene in fair yield. ... 

Cassaday (1950), Shostakovski et al. (1951) and Melnikov et al. (1952) investigated extensively the addition reactions of dialkyl phosphorodithioic acids to unsaturated dicarbonic acid esters, and found that the dialkyl phosphorodithioic acids are added at the double bond in the same way as are mercaptans. This reaction was used by Cassaday (1950) who prepared 0,0-dimethyl-S-(l,2-dicarbethoxy)-ethyl phosphorodithioate by the addition reaction of dimethyl phosphorodithioic acid and maleic acid diethyl ester. This compound, known by the name malathion (89), became one of the most important phosphorus ester insecticides because of its low toxicity to warm-blooded animals. 

Polyesters contain carboxylic ester linkages (-0-C0-) in the backbone. Polyesters are synthesized by reaction of a diol and a dicarbonic acid, e.g. poly(ethylene terephthalate) (PET) by polycondenastion of ethylene glycol and dimethyl terephthalate. Poly(butylene terephthalate) (PBT) is produced by reaction with butylene glycol. Structures of PET and PBT are shown in Fig. 2.2.7. 

Corresponding tetramethoxy-substituted pentamers 344, 345 and a hexamer 347 were synthesized starting from 3,3"-dimethoxy-a-terthiophene 342. Pd(0)-catalyzed coupling of the bis-stannylated terthiophene with 2-iodo-3-methoxythiophene 343 results in quinquethiophene 344 (62% yield). This is subsequently lithiated and methylated in the terminal a-positions with n-BuLi/DMS to form pentamer 345 in 80% yield [Eq. (89)]. Monomethylated terthiophene 346 obtained in 81% yield from 342 with the same procedure was dimerized with the system -BuLi/Fe(acac)3 to the letramethoxy,dimethyl-substituted hexamer 347 in 70% yield [Eq. (90)]. The quaterthiophene dicarbonic acid 341 was obtained from the tetramer 335 by reaction with n-BuLi/C02 in nearly quantitative yield. 

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