Carbonyl groups polyketones

Polyketones in which two or more contiguous carbonyl groups have rings attached at each end... 

As pointed out in the introduction, because of the ease with which the carbonyl group can be chemically modified, the polyketones should be excellent starting materials for the synthesis of other classes of functionalized polymers. Indeed, a large number of derivatives of the C2H4—CO copolymer has been prepared and, not surprisingly, the vast majority of these are described in the patent literature. Patents concerning the use of these derivatives in polymer blends have also appeared but these are outside the scope of this review. 

Polyketones in which two or more contiguous carbonyl groups have rings attached at each end may be named (1) by the radicofunctional method or (2) by substitutive nomenclature. For example,... 

The coordination polymerisation of carbonyl monomers by their carbonyl group concerns mostly acetaldehyde, trichloroacetaldehyde, propionaldehyde and butyraldehyde. One basic problem with all polyaldehydes, and especially with polyketones, is not the polymerisation itself but the stabilization of resulting polymers (or copolymers) against thermal degradation. 

To the best of our knowledge, only two papers on the oxidation of polyketonates have been published. Lintvedt and coworkers have observed that the binuclear complex Co2(dbba)2py4 (136) reacts with O2 in pyridine/benzene affording the binuclear derivative 137, derived from the oxidation of the 4-methyne carbon of both ligands to carbonyl groups (equation 87). At variance with the S-diketonates, which are decomposed upon oxidation at the methyne carbon atom (Section 1V.A.2), the CH2 C=0 oxidation at C4 in the tetraketonato complex does not destroy the dianion character of the ligand, preserving the complex coordination. 

Also, the carbonyl group can be derivatized to a variety of interesting new materials. Significant advances in technological synthesis and processing made by Shell over the past decade have now moved aliphatic polyketones to commercial reality [2]. 

In summary, chain propagation involves alternating reversible carbon monoxide insertion in Pd-alkyl species and irreversible insertion of the olefin in the resulting Pd-acyl intermediates. The overall exothermicity of the polymerization is caused predominantly by the olefin insertion step. Internal coordination of the chain-end s carbonyl group of the intermediate Pd-alkyl species, together with CO/olefin competition, prevents double olefin insertion, and thermodynamics prevent double CO insertions. The architecture of the copolymer thus assists in its own formation, achieving a perfect chemoselectivity to alternating polyketone. 

Most of the natural isocoumarins are derived biosynthetically from acetate via the acetate-polymalonate pathway 293, 294). Mellein (19) is formed from acetate and malonate, as in Scheme 3 140). The early reduction of two of the carbonyl groups in the polyketone chain has been indicated by results of CD3COOH feedings ). Loss of the oxygen function at C-6 of an isocoumarin is quite common but loss of the hydroxyl group at C-8 never occurs in those isocoumarins derived from acetate, presumably as a consequence of the cyclization mechanism 293). 

A cis-coordinating ligand is apparently required to bind and activate MeOH so that a methoxy group is transferred to the polyketone chain and a hydride remains on palladium. Two mechanisms are possible for this reaction (i) nucleophilic attack by the oxygen at the acyl carbonyl with concerted formation of Pd-H (ii) formation of a Pd(acyl) (methoxy) complex and H, followed by reductive elimination and subsequent proton attack on a Pd center. No experimental evidence favoring either mechanism in ethene/CO copolymerisation has been provided so far. 

In their simplest form, polyketides are natural compounds containing alternating carbonyl and methylene groups ( p-polyketones ). The biosynthesis of polyketides begins with the condensation of a starter unit (typically, acetyl-CoA or propionyl-CoA) with an extender unit (commonly malonyl-CoA or methylmalonyl-CoA, followed by decarboxylation of the extender unit (/, 2) (Fig. 1). Repetitive decarboxylative condensations result in lengthening of the polyketide carbon chain, and additional modifications such as ketoreduction, dehydratation, and enoylreduction may also occur (discussed below). 

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