Conjugate addition reagents

Conjugate Addition. Reagent (1) in THE adds in 1,2-fashion to Q , -unsaturated ketones, whereas in THF/HMPA, 1,4-addition is observed as result of kinetic control (eq 4) The hindered Q , -unsaturated ketone isophorone gave smooth 1,2-addition in THE (89%), while in THF/HMPA, 1,2- and 1,4-addition occurred (1 1) in low conversion. 1,2-Addition of (1) to acrolein afforded a building block for bongkrekic acid. 1,4-Addition of (1) to j" -(dienyl)Fe(CO)3 substituted alkylidene malonates is highly stereoselective. ... 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

CONJUGATE ADDITION OF ORGANOCOPPER REAGENTS TO a,p-UNSATURATED CARBONYL COMPOUNDS... 

The preparation and some synthetic applications of lithium dialkylcuprates were described earlier (Section 14 11) The most prominent feature of these reagents is then-capacity to undergo conjugate addition to a p unsaturated aldehydes and ketones... 

Conjugate acid (Section 1 13) The species formed from a Brpnsted base after it has accepted a proton Conjugate addition (Sections 1010 and 1812) Addition reaction in which the reagent adds to the termini of the con jugated system with migration of the double bond synony mous with 1 4 addition The most common examples include conjugate addition to 1 3 dienes and to a 3 unsaturated car bonyl compounds... 

The methodology used in the preparation of RU 486 (84) and other ll -steroids is shown. Conjugate addition of a cuprate reagent to the a,P-unsaturated epoxide (85) provides the liP-substituted steroid (86) stereospecificaHy (131). Subsequent steps lead to the synthesis of RU 486 (84). 

Kharasch has shown that the presence of a small amount of cuprous chloride favored the conjugate addition of Grignard reagents to a, -un-saturated ketones rather than 1,2-addition. 

House investigated the role of cuprous ions in the conjugate addition of organometallic reagents. He found that the catalytic effect can be explained by the intervention of a methyl copper derivative, which reacts rapidly with the carbon-carbon double bonds of the conjugated system. 

The sesquiterpenoid hydrocarbons (5)-a-curcumene (59) and (5)-xanthorrhizol (60) were prepared by asymmetric conjugate addition of the appropriate aryllithium reagent to unsaturated oxazoline 56 to afford alcohols 57 (66% yield, 96% ee) and 58 (57% yield, 96% ee) upon hydrolysis and reduction. The chiral alcohols were subsequently converted to the desired natural products. ... 

In contrast to these ring-opening reactions, it was observed by Horner and Schwahn that 4-arylidene-(isopropylidene and cyclo-hexylidene)-oxazolones react with alkyl Grignard reagents by conjugate addition to give saturated azlactones 29a as the only products [Eq. (18)]. 

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