Mauleón Pablo, Núñez Angel A, Alonso Inés, Carretero Juan C
Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Spain.
Chemistry. 2003 Apr 4;9(7):1511-20. doi: 10.1002/chem.200390173.
Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions (Pd(OAc)(2) as catalyst, Ag(2)CO(3) as base in DMF at 120 (0)C) takes place mainly by a cascade process, involving one unit of the alkene and three units of the aryl iodide, to afford a substituted 9-phenylsulfonyl-9,10-dihydrophenanthrene. The dominant formation of this 3:1 coupling product, instead of the Heck trisubstituted olefin, shows that aromatic C-H bond activation processes can compete with the usually fast syn beta-hydrogen elimination step in the Heck arylation of an acyclic olefin. The structural scope of this palladium-catalyzed cascade arylation of alpha,beta-unsaturated sulfones has proved to be wide with regard to substitution at the beta-position (alkyl, aryl, or alkenyl substitution), substitution at the sulfone unit (alkyl or phenyl sulfones), and configuration at the CdoublebondC bond (trans or cis). Moreover, although less favored than in the case of the arylation of alpha,beta-unsaturated sulfones, similarly substituted 9,10-dihydrophenanthrenes have also been obtained in the case of alpha,beta-unsaturated phosphine oxides and alpha,beta-unsaturated phosphonate esters. A Pd(0)-Pd(II)-Pd(IV) mechanistic pathway involving the successive formation of highly electrophilic sigma-alkylpalladium intermediates and palladacycles is proposed for this multicomponent arylation.
与传统使用的无环1,2 - 二取代烯烃不同，α,β - 不饱和苯砜与芳基碘化物在Heck反应条件下（以Pd(OAc)₂为催化剂，Ag₂CO₃为碱，在DMF中于120℃）的反应主要通过级联过程进行，该过程涉及一个烯烃单元和三个芳基碘化物单元，以生成取代的9 - 苯基磺酰基 - 9,10 - 二氢菲。这种3:1偶联产物的主要形成，而非Heck三取代烯烃，表明芳香C - H键活化过程可以与无环烯烃Heck芳基化中通常快速的顺式β - 氢消除步骤相竞争。事实证明，这种钯催化的α,β - 不饱和砜的级联芳基化在β位取代（烷基、芳基或烯基取代）、砜单元取代（烷基或苯基砜）以及碳 - 碳双键构型（反式或顺式）方面具有广泛的结构范围。此外，尽管不如α,β - 不饱和砜芳基化那样有利，但在α,β - 不饱和氧化膦和α,β - 不饱和膦酸酯的情况下，也获得了类似取代的9,10 - 二氢菲。针对这种多组分芳基化，提出了一种涉及依次形成高亲电性σ - 烷基钯中间体和钯环的Pd(0) - Pd(II) - Pd(IV) 机理途径。
