Oxidative dicarbonylation

The second type is oxidative dicarbonylation of acetylene with PdCb in benzene, which produces chlorides of maleic, fumaric and muconic acids [130], Methyl maleate (215), fumarate (216) and muconate (217) are obtained in MeOH containing thiourea by passing acetylene and oxygen in the presence of a catalytic amount of PdCb [131]. 

Formation of these products can be understood by assuming that the carbonylation of propargyl alcohol under high pressure involves two different reaction pathways. One is the Pd(0)-catalyzed carbonylation and the other is the Pd(II)-catalyzed oxidative carbonylation 2,3-Butadienoate (80) is a primary product of the Pd(0)-catalyzed carbonylation, but further attack by carbon monoxide at the central sp carbon of 80 under high carbon monoxide pressure yields itaconate (81) as the dicarbonylation product. Formation of aconitate (83) is explained by the oxidative dicarbonylation of a triple bond with Pd(II) species, followed by Pd(0)-catalyzed allylic carbonylation. As a supporting evidence, methyl aconitate (83) was... 

Palladium/graphite in combination with copper(ll) chloride and flthium chloride is a good catalytic system for the oxidative dicarbonylation of alkenes using a 20 1 ratio of CO/O2 (Eq. 16). The ratio of diester to dimethyl carbonate is sensitive to the nature of the palladium catalyst precursor (Pd/graphite or PdCl2). 

The oxidative dicarbonylation of 1,3-butadiene to generate dimethyl hex-3-ene-l, 6-dioate resulted using Pd/graphite, in combination with CUCI2 and LiCl (Eq. 20). ... 

Oxidative carbonylation was coupled with reduction to afford catalytic carbonylation (see also Sect. VI.4.4.2). Thus, the diethylacetal of 2-propynal was carbonylated in a 65% yield by combining oxidative dicarbonylation and reductive splitting of an ethoxy group (Scheme 34). 

These reactions are likely to be initiated by Pd—CO2H species, formed by H2O attack on coordinated CO (Scheme 4). Formation of the maleic anhydrides corresponds to oxidative dicarbonylation and occurs with elimination of Pd(0), so the presence of an external oxidant such as O2 is required to make the process catalytic. On the other hand, a Pd—H species [in equilibrium with Pd(0) + H+] may be responsible for double bond reduction leading to succinic anhydrides. 

Cyclocarbonylation of unsaturated substrates incorporating a nucleophilic function (—YH) in a suitable position can also be effected in the presence of external nucleophiles (ZH) such as alcohols. These reactions usually result in oxidative dicarbonylation of the unsaturated bond and are promoted by Pd(ll) species. As ensuing dicarbonylation Pd(ll) is reduced to Pd(0), the presence of an oxidant is needed in order to make the process catalytic, as exemplified in Scheme 18 in the case of triple bond. 

Endoperoxides (also 1,2-dioxetanes) are versatile starting materials for further transformations. In view of the weak 0-0 bond, these peroxides are thermally sensitive to homolytic cleavage, a feature that makes most of them ha2aidous. Ring opening opens up attractive opportunities for selective transformations that include reductions (diols), oxidations (dicarbonyl products), rearrangements (hydroxy carbonyl compounds, epoxy carbonyl compounds, fo/s-epoxides, ene diones, etc.) and additions (polycycKc dioxanes or trioxanes, some of which display antimalarial activity). The synthesis and the subsequent reactions of the 2,3-dioxabicyclo[2.2.2]oct-7-en-5-one skeleton have been studied by Adam etak An impressive number of chemical transformations and examples for applications in organic synthesis have been collected in several reviews. 

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