Allylic derivatives regiochemistry

Goering, H. L. Seitz, E. P. Tseng, C. C. Alkylation of allylic derivatives. 3. The regiochemistry of alkylation of the isomeric trans-a,y-methylphenylallyl acetates with lithium dialkylcuprates./. Org. Chem. 1981, 46, 5304— 5308. 

Cycloaddition of CO2 with the dimethyl-substituted methylenecyclopropane 75 proceeds smoothly above 100 °C under pressure, yielding the five-membered ring lactone 76. The regiochemistry of this reaction is different from that of above-mentioned diphenyl-substituted methylenecyclopropanes 66 and 67[61], This allylic lactone 76 is another source of trimethylenemethane when it is treated with Pd(0) catalyst coordinated by dppe in refluxing toluene to generate 77, and its reaction with aldehydes or ketones affords the 3-methylenetetrahy-drofuran derivative 78 as expected for this intermediate. Also, the lactone 76 reacts with a, /J-unsaturated carbonyl compounds. The reaction of coumarin (79) with 76 to give the chroman-2-one derivative 80 is an example[62]. 

As expected, allylic alcohols and ethers afford v/c-diol derivatives upon hydroboration. However, in the presence of Wilkinson s catalyst, a reverse regiochemistry for the hydroboration is observed [108]. There is the possibility that boron, rather than hydrogen, is transferred from the metal to the olefin. In other words, the boron acts as a donor. 

The nature of the ligands on the palladium in ir-allyl complexes can influence the regioselectivity exhibited by soft carbon nucleophiles. ir-Allylpalladium complexes generated from methylenecycloalkanes provide an example of the effect of ligands on regiochemistry. The complexes derived from methylene-cyclopentane and methylenecycloheptane both exhibit exclusive exocyclic addition by the anion of methyl(methylsulfonyl) acetate with triphenylphosphine ligands on the Pd (equation 223). In contrast, the complex derived from methylenecyclohexane yields a 62 38 ratio of exocyclic endocyclic addition (equation 226). 

E.3.2.1. Deracemization of Acyclic Substrates When chiral allylic substrates generate meso 71-allyl intermediates, the two allylic termini of such intermediates are enantiotopic. Thus, enantioselectivity is derived from the regiochemistry of the nucleophilic addition (a vs. b), and the alkylation process corresponds to a deracemization event (Eq. 8E,2). One of the prototypical reactions, which has been studied in extensive detail, is the 1,3-diphenylallyl system. Since its introduction as a different mechanistic motif in contrast with the 1,1,3-triphenylallyl system, this reaction has become a benchmark for design and comparison of a variety of different ligands in recent years [73]. 

Steroids which react with azide ion by competing S nI and Sjj2 mechanisms do not give products of controlled regiochemistry and configuration. 3jS-Chloro-4-cholestene (80), for example, when treated with sodium azide in dimethyl sulphoxide , affords mosdy 2,4-cholestadiene (81), which arises by loss of the 2-proton from the allylic carbonium ion intermediate (82). The substitution product, isolated as the 3-acetamido derivative after reduction of the azide and... 

Dienes substituted with heteroatoms, X or Y in 145, give allyl (Y in 146) or vinyl (X in 146) derivatives by the Diels-Alder reaction. The heteroatom(s) not only provide latent functionality in the product but also control the regiochemistry of the Diels-Alder reaction itself86. In Danishefsky s vemolepin synthesis87, a compound of type 146 was converted into an enone 147 by hydrolysis since 146 is a 1,3-disub-stituted allyl compounds like the enone precursors in the last section. 

The Larock method for annulation between vicinal iodo-arylamines and 1,2-dienes in the preparation of indoles can be adapted for preparation of azaindoles using corresponding azine substrates. Thus, substituted-3//-pyrrolo[2,3-fc]pyridin-3-ones can be prepared from 2-amino-3-iodopyridine derivatives by a palladium carboannulation process with al-lenic compounds (Scheme 104). The bicychc products, the methylene derivatives 308, and the alkylidenes 309 can be oxidatively cleaved with ketone formation. The reaction may proceed by formation of a pyridinylpaUadium complex followed by the rr-allyl complexa-tion of aUenic derivatives 310. Since the polar substituents on terminal carbons of the 7r-allyl system influence the regiochemistry of the reactions, nucleophilic attack of the nitrogen atom on the most electron-deficient carbon atom of the rr-allyl system affords either of the... 

A nickel-catalyzed carbozincation in which an allylzinc adds across the double bond of an unsaturated acetal has also been reported (Scheme 79). ] This procedme effectively provides a reverse-polarity approach to the functionalization of unsaturated carbonyl derivatives. Non-allylic Grignard reagents, however, add to cychc unsaturated acetals with the opposite regiochemistry. This latter procedure provides the basis for an enantioselective conjugate addition to cyclic enones (in 53% ee for the cyclopentenyl substrate and 85% ee for the cyclohexenyl homologue). ... 

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