Coupling with allyl halides

The first carbon—carbon bond-forming reaction of zirconacyclopentadienes involving a copper transmetalation was the double allylation reaction shown in Eq. 2.33 [6]. 

When the electrophile contains two allyl halide moieties, two carbon—carbon bonds are formed, resulting in cyclized compounds 47 and 48, as shown in Eq. 2.34 [7f]. 

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Perfluoroalkylzinc iodides, prepared in situ from iodides and ultrasonically dispersed Zn, are coupled with allylic halides via an allylic rearrangement[271]. The Pd-catalyzed homocoupling of allylic acetate in the presence of Zn to give a mixture of regioisomers 416 and 417 may proceed via in situ formation of allylzinc species[272,273]. 

The transmetalation of dialkenylchloroboranes of type 52 with methylcopper (3 equiv.) provides an alkenylcopper compound 53, which undergoes cross-coupling with allylic halides to produce mixtures of Sn2 and Sn2 products. Interestingly, this method is also useful for the preparation of functionalized alkenylcoppers such as 54 (Scheme 2.14) [31]. 

Electrophiles also react at C-5 of 1,3-dioxin-4-ones. Two ways of activation have been reported (1) magnesiation of 5-iodo-l,3-dioxin-4-ones afforded the Grignard reagents which can be cross-coupled with allyl halides in the presence of copper cyanide <2001TL6847> or with iodoalkenes under Pd(0) catalysis <2002T4787> and (2) Sc(OTf)3-catalyzed reaction of a side-chain-hydroxylated l,3-dioxin-4-one with aldehydes provided the bicyclic dioxinone in 60-85% yield (Scheme 27) <20050L1113>. 

Alkenyl-aluminum and -zirconium derivatives have been found to couple with allyl halides in the presence of Pd° catalysts (equation 38), although simple alkyl-aluminum and -zirconium reagents fail in the reaction.154 The 1,4-dienes thus generated are important intermediates in organic synthesis. 

Active copper powder. A highly reactive copper powder can be prepared by reduction of Cut with potassium naphthalenide in DME (8 hours). The slurry should be used immediately. It is particularly effective for Ullmann reactions high yields of biaryls are obtained even at 85°. It also promotes cross-coupling with allyl halides. ... 

When dialkylcopperzinc reagents R2CuZnCl couple with allylic halides, almost complete allylic rearrangement occurs (Sn2 )> and the reaction is diastereoselective if the allylic halide contains a 8 alkoxy group. Another type of copper reagent... 

Addition-coupling sequences. The addition of organometals to alkynes in the presence of NiCacac) generates alkenylmetals which can be used to couple with allylic halides directly (in cases of Al) or after exchange with Cu (in cases of Zn) . 1,4-Dienes are formed. 

The BiBrs-Sm binary reagent promotes reductive C-S and C-Se bond formation between benzyl and allyl bromides and diorganyl disulfides and diselenides in aqueous media, affording the corresponding sulfides and selenides, respectively (Scheme 14.105) [217, 218]. Intramolecular reductive C-S bond formation by use of a BiCl3-M (M = Sn, Zn) redox system is used in the synthesis of 3-hydroxyceph-ems and 2-exo-methylenepenams (Scheme 14.106) [219]. Alkyl and arylsulfonyl chlorides couple with allylic halides in the presence of Bi to afford the corresponding allylic sulfones [220]. 

Further, the presence of an electron-withdrawing group on the Ji-allylic ligand was found to favor cross-coupling with allyl halides (Chiusoli, 1971). 

Alkylthioallyl-lithium reagents couple with allylic halides by a-a ( head-to-head ) coupling, whereas the corresponding alkylthioallyl copper compounds couple y-y ( tail-to-tail ). Allylic bromides can now be coupled with the lithium alkylthioallyl borate complex [viz. (78)] to give the 1,5-diene (79). The 9-BBN-ate complex gives a better yield and regiospecificity than the corresponding tri-n-butyl borate. 

Negishi and his co-workers have developed several approaches to allylated arenes involving cross-coupling reactions. Preliminary studies established that aryl-aluminium, zirconium, or zinc compounds readily undergo palladium-catalysed cross-coupling with allylic halides or acetates (Scheme 19). Later in the year it was shown that allylic alcohol derivatives containing OAlR2,... 

Alkenyl-aluminium or -zinc species cross-couple with allylic halides or derivatives of allylic alcohols (c.g. acetates or phosphates) under the influence of Pd(PPh3)4 to give 1,4-dienes. In favourable examples coupling occurs with complete retention of stereo- and regio-chemistry of both alkenyl and allyl substrates, and it is free from formation of homocoupled products (Scheme 73). However, partial allylic inversion was observed in reactions involving E-crotyl... 

Castro-Stephens-like Coupling with Allylic Halides... 

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