Reactions involving allyl carbonates

In a recent development, Castano and Echavarren [42] have described couplings of allyl carbonates with alkenyl (and aryl) tins Pd2(dba)3 is used as the catalyst. These reactions are 

---

Intramolecular anodic olefin coupling reactions involving allyl- (equation 18) and vinyl-silanes (equation 19) can lead to good yields of quaternary carbons with control of the relative stereochemistry19,20. This is the first example of an electrochemical reaction that makes use of a temporary silicon tether. 

Ruthenium complexes are also suitable catalysts for carbonylation reactions of a variety of substrates. Indeed, when a reaction leads to C-Ru or het-eroatom-Ru bond formation in the presence of carbon monoxide, CO insertion can take place at the coordinatively unsaturated ruthenium center, leading to linear ketones or lactones. Thus, ruthenium-catalyzed carbonylative cyclization was involved in the synthesis of cyclopentenones by reaction of allylic carbonates with alkenes in the presence of carbon monoxide [124] (Eq. 93). 

The reaction of allyl carbonates with 2-norbornene under 3 atm of CO catalyzed by [RuCl2(CO)3]2 gives cyclopentenones. A reaction mechanism involving successive insertion of 2-norbornene and CO into a Jt-allyl-ruthenium bond is proposed (Eq. 11.39) [83], the details of which discussed in Chapter 5. 

Carbon-Carbon Bond Formation Reactions Involving Allyl-Ruthenium Intermediates. Unlike many other allylmetal complexes, r-allyl-ruthenium complexes demonstrate both nucleophilic and electrophilic behavior. Two postulated mechanisms are presented side by side in Figure 23. The first scheme shows the mechanism for nucleophilic addition of primary alcohols to allyl... 

A brief overview of the well-established chemistry of Pd-catalyzed carbon-carbon bondforming reactions involving allylic and propargylic compounds is presented. 

It has recently been suggested (19) that 7r-allylnickel complexes are intermediates in reactions involving allylic halides. Although ir-allylnickel chloride-triphenylphosphine (IX) is formed from allyl chloride and Ni(CO)3P(C6H5)3 without jrielding a carbonylation product (20), the dimeric 7r-allylnickel chloride (X) [prepared (13) by heating allyl chloride with nickel carbonyl in benzene solution] reacts rapidly with carbon monoxide to form butenoylnickel dicarbonyl chloride (XI) (Eq. 13). Moreover, this complex is converted by additional carbon monoxide into butenoyl chloride and nickel carbonyl (13), Eq. (14)... 

The intermolecular carbon-carbon bond forming reaction involving allylic sulfones has also been considered without mediators. The successful addition of 2-functionalized allyl sulfones to vinylacetate, taking advantage of favorable polar effects, has been performed by Whitham and co-workers (equation (70))... 

Another reaction involving a carbonate is the reduction of allylic substrates in the presence of formic acid. This reaction has been described in an asymmetric manner, in the presence of aJlylpalladium chloride dimer 1 and (/J)-MeO-MOP as the chiral ligand (eq 16) The resulting ester is isolated in high yield and 87% enantiomeric excess. The mechanism was studied in the presence of an analog of (/J)-MeO-MOP ligand. ... 

Barluenga and coworkers utilized a dilithiation reaction involving allylic amines to prepare 3- and 4-substituted 3-pyrrolin-2-ones (1988TL4859, 1993TL7777). Sequential treatment of allylic amines (e.g., 247) with -butyIlithium, teri-butyllithimn and then diethyl carbonate gives 3-pyrro-Un-2-ones (e.g., 249), presumably via dilithiated intermediates such as 248 (Scheme 61). Yus and coworkers used CO2 as an electrophile in a similar sequence used to prepare l,5-dimethyl-4-phenyl-3-pyrrolin-one (1995 TA2081). 

In contrast to oxidation in water, it has been found that 1-alkenes are directly oxidized with molecular oxygen in anhydrous, aprotic solvents, when a catalyst system of PdCl2(MeCN)2 and CuCl is used together with HMPA. In the absence of HMPA, no reaction takes place(100]. In the oxidation of 1-decene, the Oj uptake correlates with the amount of 2-decanone formed, and up to 0.5 mol of O2 is consumed for the production of 1 mol of the ketone. This result shows that both O atoms of molecular oxygen are incorporated into the product, and a bimetallic Pd(II) hydroperoxide coupled with a Cu salt is involved in oxidation of this type, and that the well known redox catalysis of PdXi and CuX is not always operalive[10 ]. The oxidation under anhydrous conditions is unique in terms of the regioselective formation of aldehyde 59 from X-allyl-A -methylbenzamide (58), whereas the use of aqueous DME results in the predominant formation of the methyl ketone 60. Similar results are obtained with allylic acetates and allylic carbonates[102]. The complete reversal of the regioselectivity in PdCli-catalyzed oxidation of alkenes is remarkable. 

Many organic chemical transformations have been carried out in ionic liquids hydrogenation [4, 5], oxidation [6], epoxidation [7], and hydroformylation [8] reactions, for example. In addition to these processes, numerous synthetic routes involve a carbon-carbon (C-C) bond-forming step. As a result, many C-C bondforming procedures have been studied in ambient-temperature ionic liquids. Among those reported are the Friedel-Crafts acylation [9] and allcylation [10] reactions, allylation reactions [11, 12], the Diels-Alder reaction [13], the Heck reaction [14], and the Suzuld [15] and Trost-Tsuji coupling [16] reactions. 

Some examples of conjugate addition reactions of allylic silanes are given in Scheme 9.5. Entries 1 to 3 illustrate the synthesis of several (3-allyl ketones. Note that Entry 2 involves the creation of a quaternary carbon. Entry 4 was used in the synthesis of a terpenoid ketone, (+)-nootkatone. Entry 5 illustrates fluoride-mediated addition using tetrabutylammonium fluoride. These conditions were found to be especially effective for unsaturated esters. In Entry 6, the addition is from the convex face of the ring system. Entry 7 illustrates a ring closure by intramolecular conjugate addition. 

Catalytic reactions involving addition of two molecules of butadiene and hydrogen transfer from an acidic carbon atom (adjacent to a ir-allyl group) to the nickel oxygen bond were recently described (example 12, Table IV). 

This reaction involves the two reactants carbon monoxide and alcohol and produces esters, or lactones. The starting material, which will be considered here, is an alkene or an alkyne but it is also possible to start from activated halides (aryl- or allyl- iodides and bromides) to produce the same kind of organic products. 

The isomerisation of allyl and propargylic alcohols involves the 1,3-shift of an oxygen atom rather than a hydrogen atom. Isomerisation of allyl alcohols can be catalysed by a variety of metal oxo complexes and in this instance the reaction does not involve metal carbon bonds as we will see. One could imagine that allylic metal species can participate in isomerisation of allylic compounds, but for the alcohols themselves this is not an easy reaction. In chapter 13 reactions of allyl acetates and the like, which are more prone to... 

---