Allylic substitutions allyl benzoates

The synthesis of lycorane (13) by Mori and Shiba-saki121 is breathtaking for its use of three consecutive Pd catalyzed C-C bond forming reactions. Thus, Pd-catalyzed asymmetric allylic substitution of a benzoate in meso 7 in the presence of the chiral bisphos-phine 8 leads to the regioselective formation of 10 in 40 % ee It is easy to overlook this low level of enantioselectivity when we are faced with the subsequent elegant Pd-catalyzed reactions Pd-catalyzed intramolecular animation is followed by a Pd-catalyzed Heck coupling to afford 12, which is then readily converted to the target molecule... 

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... 

An equimolar (10 mmol) mixture of benzoyl chloride and n-butyl oxide adsorbed on 5 g graphite A was sequentially irradiated with 90 W incident power. The conversion reached 80% (Yield of isolated n-butyl benzoate (69) 62%). With ethyl oxide, the yield of ethyl benzoate (68) was lower, but noteworthy considering the volatility of this oxide, and the significant retentive power of graphite towards organic compounds. These preliminary results have not yet been expanded, but it is certain that more reactive ethers, like those substituted with sec- or teri-alkyl, benzylic or allylic groups, are deavable in the same way. 

Usually, treatment of the crude stannylene with benzoyl chloride for a few minutes at room temperature gives one of the two possible benzoates, in very high yield, in a regioselective manner. Allyl and benzyl halides do not react under these conditions, and they react only sluggishly in refluxing nonpolar solvents. Substitution proceeds in a satisfactory manner in the presence of 5-10 mol% of a quaternary ammonium bromide or iodide. Alternatively, the stannylene may be transferred into N, IV-dimethy lformamide, in which substitution occurs at 80°C. Again, allylation and benzylation of polyhydroxy lated compounds is regioselective by these methods. 

Lanthanide Lewis acids catalyze many of the reactions catalyzed by other Lewis acids, for example, the Mukaiyama-aldol reaction [14], Diels-Alder reactions [15], epoxide opening by TMSCN and thiols [14,10], and the cyanosilylation of aldehydes and ketones [17]. For most of these reactions, however, lanthanide Lewis acids have no advantages over other Lewis acids. The enantioselective hetero Diels-Alder reactions reported by Danishefsky et al. exploited one of the characteristic properties of lanthanides—mild Lewis acidity. This mildness enables the use of substrates unstable to common Lewis acids, for example Danishefsky s diene. It was recently reported by Shull and Koreeda that Eu(fod)3 catalyzed the allylic 1,3-transposition of methoxyace-tates (Table 7) [18]. This rearrangement did not proceed with acetates or benzoates, and seemed selective to a-alkoxyacetates. This suggested that the methoxy group could act as an additional coordination site for the Eu catalyst, and that this stabilized the complex of the Eu catalyst and the ester. The reaction proceeded even when the substrate contained an alkynyl group (entry 7), or when proximal alkenyl carbons of the allylic acetate were fully substituted (entries 10, 11 and 13). In these cases, the Pd(II) catalyzed allylic 1,3-transposition of allylic acetates was not efficient. 

Umpolung substitutions in which allylic or propargylic benzoates are converted into nucleophiles are realized in the presence of diethylzinc. 

Meisenheimer et were the first to study the kinetics of allylic ester isomerizations. They followed the isomerization of a-phenylallyl p-nitroben-zoate and a-phenylallyl 3,4,5-tribromobenzoate to the corresponding cinnamyl benzoates by a tedious analytical procedure involving use of melting point-composition diagrams. They observed that isomerization of the molten esters at 137°C is autocatalytic due to partial slow decomposition of the esters to substituted benzoic acids and unidentified products, and demonstrated that the reaction is catalyzed by added benzoic acids. The rate law for these reactions is... 

Reactivities of allyl esters in the radiation-induced telomerization with carbon tetrachloride. Inter alia, it was found that substituted benzoates react more rapidly than substituted phenylacetates. Esters of stronger acids reacted more slowly that those of weaker acids. It was postulated that a C—H- TC interaction prevents allyl esters fix>m interaction with CCI3 radicals [124]. 

An acid chloride functionalized liquid crystalline material was tried to bond to the silanol group in silica. The direct reaction does not seem to be successful also, a spacer with a substituted dichlorodimethyl silane is not successful. The reaction scheme is shown in Figure 16.8. However, a separation performance is observed rather by deposition than by bonding of the liquid crystals. The liquid crystalline materials used in this study was based on cholesteric moieties. It is suspected that the reaction failed because of the large size of the cholesteryl group. In another study, dimeth-ylchlorosilane was added to the allyl group of 4-methoxyphenyl-4-allyloxy benzoate. This intermediate could be bonded to silica. Several other routes to fix liquid crystalline moieties on silica have been reviewed. ... 

To address the remarkable ot-substituted effects, the Pd-catalyzed allylation of benzaldehyde with a,p- and p,y-disubstituted allylic benzoates has been investigated. Using MBH adducts as substrates, a-methylene-8-butyrolactones (cis-lVt) were obtained exclusively via Pd-catalyzed allylation and spontaneous... 

Zincioester 7 (n = 0) undergoes a smooth carbonylative coupling reaction with a variety of allyl benzoates to give unsymmetrical ketones 8 in good yields (Table 2). Unsymmetrically substituted allylic benzoates provide the ketones with the lowest number of substituents at the position a to the keto carbonyl. y-Zincioester 7 (n = 1) displays apparently different reactivity from /3-zincioester, and the reaction is somewhat complicated. For the reaction with cinnamyl benzoate, the branched isomer 9 is obtained in a comparable amount to the straight chain isomer 8 (run 5). Furthermore, the reactions with allyl benzoate and cinnamyl benzoate provide considerable amounts of the doubly allylated products 10 (runs 2 and 5, in Table 2). The formation of 10 can be completely suppressed by performing the reaction in the presence of trimethylsilyl chloride, and 8 is obtained in better yields. ... 

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