Carbon dioxide synthetic equivalent

The preparation of carbonates is mechanistically closely related to the synthesis of carbamates, and similar reagents can be used for this purpose (Table 14.10). Resin-bound alcohols can be directly converted into carbonates by treatment with a chloro-formate (see Experimental Procedure 14.2), in two steps by activation with phosgene or a synthetic equivalent thereof followed by reaction with an alcohol in the presence of a base, or by treatment of a resin-bound alcohol with carbon dioxide and an alkyl halide under basic reaction conditions [125]. Thiocarbonates can be prepared from... 

In this chapter, we discuss the need and the possibilities of catalytic activation of carbon dioxide as well as its most important reactions of synthetic utility. Although important in research and in chemical industry, the reactions that produce expensive waste in an equivalent amount to the desired product (such as Grignard carboxyla-tions and electrochemical reactions with reactive anodes (Al, Mg)1) are not discussed. Photosynthesis and enzymatic CO2 activation are not included either, because in their complexity natural processes are so far from the reactions investigated and practiced in synthetic systems that there are only a few points of immediate cross-fertilization of ideas (although such interactions between the fields can be highly rewarding). 

Camphor, 14, 139 Cannabinoid, 198 Cannabinol, 197 Carbodiimide, 266 Carbohydrate pseudoglycal, 98 p-Carbomethoxynitrosobenzene, 74 Carbon dioxide, 193 synthetic equivalent of, 101 Carbon monoxide, 193 o,/3-Carbonyl compounds, unsaturated, 169-187... 

Ruden and Bonjouklian have suggested that ketomalonate might serve as the synthetic equivalent of carbon dioxide, which itself does not react as a dienophile.21 They have found that adducts can, in fact, be transformed via a Curtius sequence into /3,-y-unsaturated lactones [Eq. (6)]. 

Gribble and coworkers [90, 91] have shown that munchnones 220 undergo dipolar cycloadditions with 2- or 3-nitro-substituted A -protected indoles 219 to give, after loss of carbon dioxide from the initial cycloadduct 221, the corresponding pyrroloindoles 222. These products are synthetic equivalents of indole 2,3-quino-dimethanes and in turn have been used as dienes in subsequent Diels-Alder reactions (see the following chapter). For munchnones that provide unsymmetrically substituted pyrroles (i.e.. Re and R7 are not same), good regioselectivity is observed in the cycloaddition reactions (Scheme 60). 

One method to prepare cyclic carbonates of the structural type shown in Scheme 44 is by direct reaction of 1,2-diols with a phosgene synthetic equivalent, but they can also be prepared by Pd(0)-catalyzed reaction of vinylepoxides with carbon dioxide. Trost and Granja have found that the behavior of vinylepoxides and their related carbonates in Pd(0)-catalyzed allylations is different from the stereochemical viewpoint. ... 

For synthetic purposes hydroxypyruvate 119 can effectively replace the natural donor components [258]. Its covalent activation occurs at a reduced rate of about 4% relative to xylulose 5-phosphate (121) but is accompanied by spontaneous decarboxylation [262]. Thus, loss of carbon dioxide renders synthetic reactions irreversible whereas alternative donors, for example l-erythrulose, require coupling to cofactor recycling to shift the overall equilibrium [263]. The thermodynamic driving force from decarboxylation of 119 is particularly useful with equilibrating multi-enzyme systems such as that used in the gram-scale synthesis of two equivalents of 121 from 42 (Figure 5.54) [264]. 

Various heterocumulenes can be used as synthetic equivalents of the synthon. In reaction with isocyanates, isothiocyanates, carbon dioxide, or carbon disulfide by the Wittig reaction, the iminophosphates 231, obtained firom o-(l-pyrrolyl)phenyl azide, form o-pyrrolylphenylheterocumulenes, which undergo cyclization to condensed pyrroloquinoxalines 155, 209k, 210, and 232 (Scheme 3.72) (Molina et al. 1989, 1990). 

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