Allyl acetates allylic transposition

Both the palladium- and the nickel-catalysis enables the use of allylic acetate as starting reagent. In the two approaches a zinc compound is evoked as key intermediate, though its formation has been demonstrated only indirectly. In the two methods allylic transposition is observed. The authors have then concluded that these electrochemical allylation reactions closely parallel the chemical allylation reactions involving allylzinc intermediates. 

With related compounds, such as allylic acetals, they react with total allylic transposition in good yields to afford the corresponding enol ethers [57 Eq. (41)]. 

Allylic substitution with borates. Arylation of allylic acetates without transposition using B-alkyl-B-aryl-l,3,2-dioxoborolidines occurs in the presence of (Ph3P)2NiCl2. Note the exclusive transfer of the aryl group. 

Vinyl—silicon bonds are also rather easily cleaved by electrophiles. It appears that the R3Si group is able to stabilize //-carbonium ions. Allylsilanes are prone to attack even by fairly weak electrophiles. Acetals, aldehydes and ketones react in the presence of Lewis acids to form unsaturated alcohols. The reaction is accompanied by an allylic transposition ... 

The research groups of Trost and Stille have demonstrated in related studies that allylic stannanes undergo palladium-catalysed cross-coupling with allylic acetates °° or allylic bromides to furnish 1,5-dienes in variable yields. The stannane undergoes predominant or complete allylic transposition during coupling with either type of substrate (e.g. Scheme 96). 

The reaction of allyl bromides with allyltin reagents, catalysed by palladium or zinc chloride, gives cross-coupled products without allylic transposition in the allyl halide partner, but with predominant allylic rearrangement from the tin partner. Similar unsymmetrical cross-couplings of allylstannanes with allyl acetates have also been observed (Scheme 19). ... 

The first example of chemoenzymatic DKR of allylic alcohol derivatives was reported by Williams et al. [37]. Cyclic allylic acetates were deracemized by combining a lipase-catalyzed hydrolysis with a racemization via transposition of the acetate group, catalyzed by a Pd(II) complex. Despite a limitation of the process, i.e. long reaction times (19 days), this work was a significant step forward in the combination of enzymes and metals in one pot Some years later, Kim et al. considerably improved the DKR of allylic acetates using a Pd(0) complex for the racemization, which occurs through Tt-allyl(palladium) intermediates. The transesterification is catalyzed by a lipase (Candida antarctica lipase B, CALB) using isopropanol as acyl acceptor (Scheme 5.19) [38]. 

Homoallylk ethers. lodotrimethylsilane catalyzes the allylation of acetals and ketals by allylsilanes, with transposition of the allylic group (equation I). It does not catalyze allylation of aldehydes and ketones. Note that TiCI can catalyze both of these reactions (7, 370-371). In this respect, ISi(CH3)3 resembles (CH3)3SiOTf (this volume). 

The rearrangement of the allylic acetate in the prostaglandin side chain (entries 3 and 4) demonstrates the influence of chirality and double-bond geometryl8- 24-25-39. Oxygen transposition in the (Z)-allylic acetate led to the (15.S (-acetate with the E configuration of the new double bond, whereas the ( )-acetate gave under similar conditions the (15R)-acetate, also with the E configuration of the double bond. 

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. 

With this bicyclic intermediate available in sizeable amounts, ready advance to 111 could be conveniently accomplished prior to annulation of the second five-membered ring (Scheme XIV). 1,3-Carbonyl transposition was realized by complete eradication of the original carbonyl by Ireland s method [60] followed by allylic oxidation. Application of the Piers cyclopentannulation protocol [61] to 111 made 113 conveniently available. Introduction of a methyl group into ring B was brought about by treatment of the kinetically derived enol triflate [62] with lithium dimethylcuprate [63], Hydrolysis of 114 gave the dienone, which was directly transformed into 115 by oxidation of its silyl enol ether with palladium acetate in acetonitrile [64],... 

McIntosh et al. have applied the Ireland-Claisen rearrangement of bis-allyl silyl ketene acetals in studies directed toward the synthesis of the eupomatilones (Scheme 4.135) [128]. The 1,2-transposition of the alkene, which occurred in the rearrangement afforded a reactive vinyl epoxide (cf Scheme 4.83). Stereoselective cyclization of the carboxylic acid onto the vinyl epoxide generated the 5-aryl lactone, which was further manipulated to the putative structure of 5-epi-eupoma-tilone-6. 

The [3,3]-sigmatropic rearrangement of allylic acetates, catalysed by soluble Pd salts, that was reported last year (4,152) as a method for [1,3]-oxygen transposition has recently been shown to occur suprafacially with complete chirality transfer an example is the conversion (70) (71). Overman has... 

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