Allyl chlorides, coupling with

Stork7 found further that the allylic chlorides couple with methallylmagnesium bromide in high yield to give 1,5-dienes provided that HMPT is used as cosolvent withTHF. 

Arylpalladium salts ArPdX prepared from arylmercury compounds and lithium palladium chloride couple with allylic chlorides in moderate yields,... 

Allylic chlorides react with organozinc halides or diorganozincs in the presence of catalytic amounts of CoBr2 [92]. These reactions lead to the 8 2 cross-coupling product with... 

Stork [11], as well as Corey [12], have shown that methallylmagnesium chloride couples with allylic chlorides affording a mixture of 8, 2 and Sn2 products. However, Stork [11] has found that the use of hexamethylphosphoramide (HMPA) as a cosolvent allows the formation of the sole 8, 2 product 10, without any rearrangement of the double bond, after reaction with either cis- or trans-chlorides 9 [Eq. (4)]. 

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]. 

Knight s synthesis of ( ) -a-kainic acid provides aheterocyclic example.38 The starting material for the Claisen rearrangement is made from natural aspartic acid coupled to an allylic chloride 198 with a protected allylic alcohol 200 also present. Deprotection and lactonisation gives the nine-membered nitrogen-containing lactone 201. 

The palladium-catalyzed cross coupling of allyl chloride 6 with vinyltributyltin occurs with net retention of configuration if the reaction is conducted under conditions that favor oxidative syn addition4, though the degree of stereoselectivity is somewhat lower than for its catalytic phenylation using a tin reagent (see Table 27). 

The total synthesis of fluvirucinine A1 127 provides a powerful illustration of the utility of Fu s methodology in natural product synthesis (Scheme 13.34). The asymmetric Negishi reaction of racemic allylic chloride 122 with alkylzinc bromide 123 in the presence of Ni/Pybox catalyst system provided ester 124 in 93% yield and 96% ee. After few steps, the organozinc reagent of bromide 125 was subjected to a second Negishi reaction with chloride 122 under identical coupling conditions to furnish derivative 126 in 80% yield and excellent enantioselectivity. 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

Coupling of allyl chloride with the (2 -alkenylpentafluorosilicate 463 using Pd(OAc)j as a catalyst at room temperature gives a 1,4-diene in good yields. The reaction has been applied to the synthesis of recifeiolide[299]. 

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

One of the most gentle methods for the generation of reactive allylmetallic reagents was introduced in 1977 by Hiyama and Nozaki1,2,3,33. By the action of two equivalents of chromi-um(II) chloride on allylic halides in tetrahydrofuran at 0°C in the presence of a carbonyl compound, reductive coupling with the formation of a homoallylic alcohol takes place. 

All examples mentioned so far correspond to reactions between two aromatic groups, however, couplings in which one or both partners are alkyl groups can be achieved using electron-rich boron-based nucleophiles. Fiirstner has reported the use of B-alkyl or 5-allyl methoxy-9-BBN anions for the efficient coupling with some aryl chlorides using an in situ prepared IPr HCl/Pd(OAc)j system [118], Some of the results obtained with these easy-to-handle borate-based nucleophiles are shown below (Scheme 6.34). 

A crystal structure of the C02 derivative of (8), K[Co(salen)( 71-C02)], haso been reported in which the Co—C bond is 1.99 A, the C—O bonds are both equivalent at 1.22 A and the O-C-O angle is 132°.125 Carboxylation of benzylic and allylic chlorides with C02 in THF-HMPA was achieved with (8) electrogenerated by controlled-potential electrolysis,126 in addition to reductive coupling of methyl pyruvate, diethyl ketomalonate and / -tolylcarbodiimide via C—C bond formation. Methyl pyruvate is transformed into diastereomeric tartrates concomitant with oxidation to the divalent Co(salen) and a free-radical mechanism is proposed involving the homolytic cleavage of the Co—C bond. However, reaction with diphenylketene (DPK) suggests an alternative pathway for the reductive coupling of C02-like compounds. 

Allylic chlorides can also be used as coupling partners, as shown by Lu and Liu [137]. In addition, the domino process could be used for the synthesis of benzylidene pyrrolidines, as shown for the reaction of 6/1-285 with benzylidene malonate... 

Trapping experiments with electron deficient olefins such as acrylonitrile and 3-buten-2-one gave the expected 1,4-adducts from the proposed acylnickel intermediates. This provides strong support for the proposed mechanism. It was also demonstrated that allylic, vinylic and pentafluorophenyl halides could be cross-coupled with acid chlorides to give the corresponding ketones in good yields. 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Lithiation of the vinylstannane moiety of 22 with BunLi followed by the reaction with PhCHO gives (Z)-7-silyl allylic alcohol 23 (Scheme 65).261 The subsequent Cu(i)-mediated cross-coupling with allyl chloride affords (Z)-allylic alcohol 24 with the (Z)-stereochemistry retained. 

Yields of the coupling products with alkynyl bromides are relatively low as compared with those obtained with allyl chloride or benzyl chloride. One reason for this is the instability of the product. The dienediynes 51 are slowly cyclized under the influence of light to give pentacyclic dimers 52 (Eq. 2.36), one of which has been characterized by X-ray analysis. 

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