Epoxides alkoxycarbonylation

Not least for the syntheses of natural products, alkoxycarbonylations with formation of allenic esters, often starting from mesylates or carbonates of type 89, are of great importance [35, 137]. In the case of carbonates, the formation of the products 96 occurs by decarboxylation of 94 to give the intermediates 95 (Scheme 7.14). The mesylates 97 are preferred to the analogous carbonates for the alkoxycarbonylation of optically active propargylic compounds in order to decrease the loss of optical purity in the products 98 [15]. In addition to the simple propargylic compounds of type 89, cyclic carbonates or epoxides such as 99 can also be used [138]. The obtained products 100 contain an additional hydroxy function. 

Abstract Development in the field of transition metal-catalyzed carbonylation of epoxides is reviewed. The reaction is an efficient method to synthesize a wide range of / -hydroxy carbonyl compounds such as small synthetic synthons and polymeric materials. The reaction modes featured in this chapter are ring-expansion carbonylation, alternating copolymerization, formylation, alkoxycarbonylation, and aminocarbonylation. 

The alkoxycarbonyl group does not have a strong directing effect on the ring opening of epoxides by amines (Scheme 4.76), and steric or electronic effects of the other substituents can be more important to the outcome of these reactions. The... 

Scheme4.76. Reactions of amines with alkoxycarbonyl-substituted epoxides [342-345].

V-Alkoxycarbonyl- and /V-carboxamido-oxaziridines (35) have been developed as reagents capable of converting aromatic alkenes into epoxide, aziridine, or hydrooxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydrooxidation with promising levels of asymmetric induction.48... 

From a methodological point of view, it should be pointed out the formation of 51, which is a result of the addition of acetone to an allenylidene ligand. Heteroatom-containing cyclic metal-carbene complexes [24] have been conveniently prepared via metal co-haloacyl, carbamoyl, alkoxycarbonyl, or imido intermediates [25], opening of epoxides by deprotonated Fischer-type carbene complexes [26], and activation of homopropargylic alcohols with low-valent d complexes [27], including ruthenium(II) derivatives [28]. In general, the preparation of unsaturated cyclic carbene complexes requires the previous preparation of functional carbenes to react with P-dicarbonyl derivatives, acrylates, and enol ethers [29]. 

This alkoxycarbonylation reaction is also catalytic, if the alkylcobalt tetracarbonyl is formed from an epoxide and cobalt carbonyl anion in a hydroxylic solvent (9). A stoichiometric amount of base is not required in this reaction. The initial product, a derivative of the anion of 2-hydroxy-ethylcobalt tetracarbonyl, may undergo three reactions (a) react with more epoxide to give polymer, (b) undergo an internal hydride shift to form aldehyde or ketone, or (c) undergo protonation, carbon monoxide insertion, and alcoholoysis (or hydrolysis) to form ester (or acid). Varying amounts of... 

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