Olefins oxidative coupling with

If anions R are oxidized in the presence of olefins, additive dimers (24) and substituted monomers (26) are obtained (Scheme 5, Table 8, and Ref. [94]). The products can be rationalized by the following pathway the radical R obtained by a le-oxidation from the anion R adds to the alkene to give the primary adduct (25), which dimerizes to afford the additive dimer (24) with regiospeciflc head-to-head connection of the two olefins, or couples with R to form the additive monomer (26). If the substituent Y in the olefin can stabilize a carbenium ion, (25) is oxidized to the cation (27), which reacts intra- or inter-molecularly with nucleophiles to give (28) or (29). 

As indicated in Scheme VII/32, cyclononanone (VII/165) is transformed into hydroperoxide hemiacetal, VII/167, which is isolated as a mixture of stereoisomers. The addition of Fe(II)S04 to a solution of VII/167 in methanol saturated with Cu(OAc)2 gave ( )-recifeiolide (VII/171) in quantitative yield. No isomeric olefins were detected. In the first step of the proposed mechanism, an electron from Fe2+ is transferred to the peroxide to form the oxy radical VII/168. The central C,C-bond is weakened by antiperiplanar overlap with the lone pair on the ether oxygen. Cleavage of this bond leads to the secondary carbon radical VII/169, which yields, by an oxidative coupling with Cu(OAc)2, the alkyl copper intermediate VII/170. If we assume that the alkyl copper intermediate, VII/170, exists (a) as a (Z)-ester, stabilized by n (ether O) —> <7 (C=0) overlap (anomeric effect), and (b) is internally coordinated by the ester to form a pseudo-six-membered ring, then only one of the four -hydrogens is available for a syn-//-elimination. [111]. This reaction principle has been used in other macrolide syntheses, too [112] [113]. 

The mechanism of the key fragmentation involves initial transfer of an electron to hydroperoxide 30 (Eq. 1.2) from Fe, forming intermediate 30a, which then cleaves homolytically to the carbon radical 30b. Oxidative coupling with Cu(OAc)2 then forms 30c in which the ester moiety is in the stable Z-configuration, stabilized by internal coordination via a psuedo six-membered ring. From this intermediate, only one hydrogen atom (Ha) is available for syn elimination and, accordingly, only the (E)-olefin is produced. 

Cp RhCl2]2 (Cp =pentamethylcyclopentadienyl)-catalysed ort/io-olefination of benzoic acid through oxidative coupling with alkenes using the oxidant Cu(OAc)2 has been achieved a,j8-unsaturated carboxylic acids also underwent olefination at the )3-position. Cine-olefination of heteroarene carboxylic acids progresses smoothly by decarboxylation to selectively produce the corresponding vinyl heteroarene derivatives. ... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Kolbe radicals can be added to olefins that are present in the electrolyte. The primary adduct, a new radical, can further react by coupling with the Kolbe radical to an additive monomer I (Eq. 9, path a), it can dimerize to an additive dimer II (path b), it can be further oxidized to a cation, that reacts with a nucleophile to III (path c), or it can disproportionate (path d). 

One other point to note in regard to this study (141) is that any evidence of oxidative addition, particularly with the chloro-olefins, was absent. The similarity of the spectra, coupled with the nonobservation of any bands in the visible region, as well as the observation of vc-c in the region commonly associated with 7r-complexation of an olefin (141, 142), all argue in favor of normal ir-coordination, rather than oxidative insertion of the metal atom into, for example, a C-Cl bond. Oxidative, addition reactions of metal atoms will be discussed subsequently. 

The proposed catalytic cycle is shown in Scheme 31. Hence, FeCl2 is reduced by magnesium and subsequently coordinates both to the 1,3-diene and a-olefin (I III). The oxidative coupling of the coordinated 1,3-diene and a-olefin yields the allyl alkyl iron(II) complex IV. Subsequently, the 7i-a rearrangement takes place (IV V). The syn-p-hydride elimination (Hz) gives the hydride complex VI from which the C-Hz bond in the 1,4-addition product is formed via reductive elimination with regeneration of the active species II to complete the catalytic cycle. Deuteration experiments support this mechanistic scenario (Scheme 32). 

Economics. Comparison of the material and energy balance for our process and the cobalt-based BASF higher olefin process (8), we foimd that our process reduced the capital investment required by over 50% due to the fact that we require far fewer unit operations, and because the operating pressure is much lower. In sutmnary, the thermomorphic solution developed by TDA allows easy catalyst recycle, which, when coupled with the lower pressure operation possible with Rh catalysts (compared to the cobalt-based process) lowers both capital and operating costs for current oxidation (oxo) plants of similar capacity. 

In most cases, the oxidative addition process consumes stoichiometric amount of Pd(OAc>2. One of the earliest examples of the use of palladium in pyrrole chemistry was the Pd(0Ac)2 induced oxidative coupling of A-methylpyrrole with styrene to afford a mixture of olefins 18 and 19 in low yield based on palladium acetate [28]. 

When furan or substituted furans were subjected to the classic oxidative coupling conditions [Pd(OAc)2 in refluxing HOAc], 2,2 -bifuran was the major product, whereas 2,3 -bifuran was a minor product [12,13]. Similar results were observed for the arylation of furans using Pd(OAc)2 [14]. The oxidative couplings of furan or benzo[i]furan with olefins also suffered from inefficiency [15]. These reactions consume at least one equivalent of palladium acetate, and therefore have limited synthetic utility. 

Examples of catalytic formation of C-C bonds from sp C-H bonds are even more scarce than from sp C-H bonds and, in general, are limited to C-H bonds adjacent to heteroatoms. A remarkable iridium-catalyzed example was reported by the group of Lin [116] the intermolecular oxidative coupling of methyl ethers with TBE to form olefin complexes in the presence of (P Pr3)2lrH5 (29). In their proposed mechanism, the reactive 14e species 38 undergoes oxidative addition of the methyl C-H bond in methyl ethers followed by olefin insertion to generate the intermediate 39. p-hydride elimination affords 35, which can isomerize to products 36 and 37 (Scheme 10). The reaction proceeds under mild condition (50°C) but suffers from poor selectivity as well as low yield (TON of 12 after 24 h). 

The formation of vinyl acetate via the oxidative coupling of ethylene and acetic acid was among the earliest Pd-catalyzed reactions developed (Sect. 2) [19,20]. Subsequent study of this reaction with higher olefins revealed that, in addition to C-2 acetoxylation, allylic acetoxylation occurs to generate products with the acetoxy group at the C-1 and C-3 positions (Scheme 14). The synthetic utihty of these products imderhes the substantial historical interest in these reactions, and both BQ and dioxygen have been used as oxidants. 

The scheme of reactions proposed to explain the products obtained is shown, after small modifications, in Scheme 8. Primary radicals 12 formed at the anodes produce with added 30 or 36 (equation lOe) the substituted benzyl or allyl radicals 38, which can dimerize to 39 or can couple with the added olefin to form radicals 40 or 41. For allyl radical (38) a 1,1 - or l,3 -coupling is possible yielding 41 and 40, respectively. Further couplings of 40 and 41 with the primary radical 12 produce 39 and head-to-tail dimer 42, respectively. It was evident from the products obtained that the coupling of 38 in the 1-position occurs 5 to 11 times faster than in the 3-position. However, for readily polymerizable olefins, rather polymerization occurs, in particular at graphite electrodes. At Pt electrodes both dimers 39 and 42 are formed, but for Cu electrodes exclusively dimers 39 were obtained with moderate yields. Thus, an indirect electrolysis including the oxidation of copper to Cu+ ions and their further reaction with 5 yielding intermediate RCu was considered, but not proved . ... 

---