cinnamonitriles_cinnamonitrile(2)

9.2.ReductiveCoupling

9.2.1.Wurtz-TypeCoupling

Homocouplingofalkylhalidesinaqueousmediacanbemediatedbymanganese/cupricchloridetogivethedimerizationproductsingoodyield.Cross-couplingcsobecontrolledtogivethedesiredproduct.632Wurtz-typecouplingofallylhalideswas(inlowyields)thenormaloutcomeinrefluxingalcohol.633Organichalidesundergoreductivedimer-ization(Wurtz-typecoupling)promotedbyzincat

ChemicalReviews,2005,Vol.105,No.83135

roomtemperatureinanaqueousmedium.634Thereactionyieldsarestronglyenhancedbyacatalyticamountofcopper.Thiscouplingprocedureprovidesanefficientandmethodforthehomocouplingofbenzylicandallylicbromidesandprimaryalkyliodides.Anallylgalliumreagentisfoundtobeeffec-tiveforradicalallylationofR-iodoorR-bromocar-bonylcompounds.Treatmentofbenzylbromoacetatewithallylgallium,preparedfromallylmagnesiumchlorideandgalliumtrichloride,inthepresenceoftriethylboraneinTHFprovidedbenzyl4-pentenoateingoodyield.Theadditionofwaterasacosolventimprovedtheyieldsofallylatedproducts.635Itwassuggestedthattheaccelerationwasduetoeitheradecreaseofthetotalvolumeofthereactantsorthetransformationofallygalliumintothemorereactiveallylgalliumhydroxide.

TheWurtz-typereductivecouplingreactionofprimaryalkyliodidesorallylhalidesandhaloorga-notinsincosolvent/H2O(NH4Cl)/Znmediaprovidesaroutetomixedalkylandallylstannanes.Forex-ample,mixedtetraalkylstannanesR3SnR′(R)Et,n-Pr,orn-BuandR′)Me,Et,n-Pr,n-Bu,orn-Pent)andR2SnR′2(R)n-BuandR′)Me,Et,n-Pr,orn-Bu)canbeeasilypreparedinaone-potsynthesisviaacouplingreactionofalkyliodidesR′IwithR3-SnX(X)Cl,I)andR2SnCl2compoundsinacosol-vent-H2O(NH4Cl)mediummediatedbyzincdust.Couplingalsooccurswith(Bu3Sn)2O.Secondaryalkyliodidesdidnotcoupleunderthesamereactionconditions.636

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