Allyl benzoate

Figure 1-17. Exciton chirality of acyclic allylic benzoates and the sign of the predicted benzoate Cotton effects. The thick line denotes the electric transition moment of the benzoate group. Reprinted with permission by Am. Chem. Soc., Ref. 61. 

In 1959, Kharasch et al.43 reported an allylic oxyacylation of olefins. In the presence of f-butyl perbenzoate and a catalytic amount of copper salt in refluxing benzene, olefin was oxidized to allyl benzoate, which could then be converted to an allyl alcohol upon hydrolysis. It is desirable to introduce asymmetric induction into this allylic oxyacylation because allylic oxyacylation holds great potential for nonracemic allyl alcohol synthesis. Furthermore, this reaction can be regarded as a good supplement to other asymmetric olefinic reactions such as epoxidation and dihydroxylation. 

Andrus et al. (109) proposed a stereochemical rationale for the observed selec-tivities in this reaction. The model is based on the Beckwith modification (97) of the Kochi mechanism, suggesting that the stereochemistry-determining event is the ally lie transposition from Cu(III) allyl benzoate intermediates 152 and 153, Fig. 13. Andrus suggests that the key Cu(III) intermediate assumes a distorted square-planar geometry. Steric interactions are decreased between the ligand substituent and the cyclohexenyl group in Complex 152 as opposed to Complex 153 leading to the observed absolute stereochemistry. 

Several methods have been described for preparing allylic zinc derivatives. In contrast to alkylzincs, allylic zinc reagents are much more reactive due to the more ionic nature of the carbon-zinc bond in these organometallics. The chemistry displayed by these reagents is not representative of the usually moderate reactivity of organozinc derivatives. Tamaru and coworkers have converted various allylic benzoates to the corresponding organozinc intermediates in the presence of palladium(O) as catalyst. 

Hydroxy-J-methoxy-5-w-propylbenzoic Acid (VI). Hydrogenation of methyl-(2-hydroxy-3-methoxy-5-allyl) benzoate (4) and subsequent saponification m.p., 119°-120.5°C. (benzene-w-hexane), yield = 80%. Elemental analysis calculated C, 62.85% H, 6.72% found C, 62.64% H, 6.80%. 

It is observed that the rate of ionization of allylic benzoates is, in most cases, inversely proportional to the pAa s of the corresponding benzoic acids, (i.e., the lower the pAa, the faster the rate of ionization.) Account for this correlation. 

A detailed kinetic study10 of a palladium-catalysed reversible cis-trans isomerization of cyclic allylic benzoates has shown how a change to a better leaving group... 

The regioselective and enantiospecific allylic substitution of alkyl-substituted allyl benzoates and carbamates with (Me2PhSi)2Zn and Cul has been shown to occur by an oxidative addition - reduction elimination mechanism rather than an SN2 mechanism.16... 

Palladium catalysed reaction of cinnamaldehyde with allyl benzoate and diethylzinc to produce ( )-1-phenyl-1,S-hexadien-3-ol66... 

The reaction has also featured in a synthesis of chrysanthemic acid (49), occlusive rearrangement occurring to give the secondary allylic benzoate (equation 21). ... 

Copper(I) salts catalyze the allylic oxidation of alkenes in the presence of peresters, such as tert-BuOjCOPh, to afford the corresponding allylic benzoate esters. In the case of terminal alkenes, internal allylic esters are formed in preference over the terminal isomers. The mechanism is believed to involve addition of an allylic radical to copper(II) benzoate. " Rearrangement of the copper(III) intermediate then produces the product and regenerates the copper(I) catalyst. 

Asymmetric allylic oxidation of alkenes using peresters is possible when the ligand L of the Cu(III) intermediate is chiral. Copper complexes of chiral bis(pyri-dine)- and bis(oxazoline)-type ligands have been used with fert-butyl perbenzoate to obtain optically active allylic benzoates. 

Acylations. Catalyzed by graphite the Friedel-Crafts acylation as well as the transformation of ethers to esters by acyl halides in refluxing 1,2-dichloroethane are realized. Although aliphatic chlorides are inferior to aromatic halides this method is quite general as shown by the synthesis of benzoates (e.g., allyl benzoate from allyl benzyl ether and methyl benzoates from methyl f-butyl ether). 

The Prevost reagent unexpectedly converts isophyllodadene (1) into the allylic benzoate (2) in good yield (1.1 g.—>0.7 g.). The same product is obtained... 

Reaction with unsaturated compounds (reviews Kharasch,Sosnovsky,andYang reported that, in the presence of a catalytic amount of a copper or cobalt salt, t-butyl perbenzoate reacts with an olefin to give an allylic benzoate with no allylic rearrangement with a terminal olefin the only product isolated was the allylic ester with a terminal double bond. A further example is the reaction with 1-methylene-4-f-butylcyclohexane. However, in contrast to these early reports, Kochi found by o... 

A useful application of the allylic benzoate CD method for determining the AC of allylic alcohols was that used for pinellic acid 7582,83 (Figure 34). Pinellic acid was isolated from Pinelliae tuber, a component of Japanese... 

Sodium hydride (60% oil dispersion, 0.15 g, 0.38 mmol) was washed with hexane (2x2 mL) and THF (1x2 mL). Note exercise great care with NaH, particularly after the hexane wash the NaH should be kept under nitrogen or argon.) To a suspension of oil-free sodium hydride in THF (5mL) was added diethylmalonate (0.770 mL, 0.38 mmol). After 15 min of stirring, the resulting diethyl malonate anion solution was added via a cannula to a solution of the allylic benzoate (131 mg, 0.56 mmol), Pd(PPh3)4 (45 mg, 0.039 mmol), and triphenylphosphine (100 mg. 

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