Reactions Involving Elimination of CO2 and Ketones

Cleavage of Carbon-Carbon Single Bonds by Transition Metals, Rrst Edition. 

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However, the previous reaction does not explain the formation of water, although for about 90% of the molecules of CO2, a corresponding molecule of water is found in the pyrolysate (some water in the pyrolysate may come from the adsorbed water on the polymer). Also, the lack of long chain hydrocarbons in the pyrolysate and the presence of aromatic compounds and of some ketones indicate that the decarboxylation process has a different mechanism. One likely possibility is the reaction involving a cyclic mechanism for the elimination of CO2 and subsequently of H2O, as shown below ... 

Other routes to oxocarbenes are the a-elimination of bromine from a,a-dibromo ketones (73JA2708, 73JA5416), and the elimination of CO2 or COS from dioxolenones (vinylene carbonates) or their sulfur analogues. The former reaction has not been investigated with regard to oxirene involvement the latter is discussed in Section 5.05.6.3.5. The formation of an oxocarbene from a chlorooxirane was mentioned in Section 5.05.6.3.2. 

The cis-1,2-addition of M-X bonds to unsaturated A=B bonds and its reverse, the -elimination of X from M-B-A-X, are fundamental elementary steps of catalytic reactions such as hydrogenation, hydroformylation, oligomerization, polymerization, hydrosilation, hydrocyanation, or alkene isomerization processes, as well as the Heck reaction. Most of the reactions described in the literature involve M-H or M-C bonds, and alkenes or alkynes. Besides them there are processes where the unsaturated substrate is different from alkene or alkyne This includes CO2, CS2, aldehydes and ketones, imine, or nitrile. Also, there are processes involving M-Si, M-Sn, M-B, M-N, M-P, or M-M bonds. The insertion of alkenes into M-carbene bonds is not essentially different in their intimate mechanism, but it is not discussed in this chapter. 

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