Diene coupling alkyl-substitution

Electron-rich olefins with substituents Y = phenyl, vinyl, amino, or alkoxy can be coupled by anodic oxidation to tail-tail dimers being either deprotonated to dienes and/or substituted a to Y, depending on Y and the reaction conditions (Eq. 6). Alkyl substituted arenes can be dehydrodimer-ized to diphenyls or diphenylmethanes depending on the kind of substitution (Eq. 7). 

The intramolecular coupKng of enolethers with enolethers, styrenes, dienes, alkyl-substituted olefins, allylshanes, and vinylshanes was systematically studied by Moeller [90,198-200]. These couplings allow the smooth formation of quaternary carbon atoms in fused bicycKc rings having a cis stereochemistry (Fig. 43) [201, 202]. 

A method for preparing specific alkyl-substituted dienyl complexes takes advantage of the propensity of (diene)Fe(CO)3 complexes to rearrange under acidic conditions, coupled with the acid-promoted dehydration illustrated earlier for the conversion of (9) to (8). Birch and Haas14 discovered that complexes derived from methylanisoles could be converted to methyl-substituted cyclohexadienyliron complexes, whose substitution pattern is defined by the relative positions of the methoxy and methyl substituents in the precursor. Several examples are given in Schemes 5 and 6 and equation (17). 

Confirmation of the preferred coupling of the primary carbon atom of the alkyl-substituted 1,3-diene has been referred to earlier, e.g., in the formation of cyclobutane derivatives from frawr-piperylene. 

One of the most elegant methods for the preparation of phosphinine proceeds through and intermediately formed trihalophosphacycloalkene (Scheme 5). When (dihalomethyl)dihalophosphines are heated with reactive dienes (e.g. alkyl-substituted buta-1,3-dienes) in the presence of excess triethylamine, the corresponding 2-halophosphinine is obtained in a simple, one-pot reaction.39,40 2-Bromophosphinine is of particular interest because it readily participates, for example, in palladium-catalysed coupling reactions.41... 

B.ii. Intramolecular Diene Coupling of Alkyl-Substituted Dienes ... 

Recently, Ni-catalyzed allylic substitutions of simple alkenes for the formation of 1,4-dienes 174 have been described by Jamison and Matsubara. Allylic alcohol derivatives 172, bearing a variety of leaving groups, can be coupled with a wide range of simple alkenes 173 including gaseous ethylene and propylene. The key for the reaction was the use of the appropriate nickel-phosphine complex and a stoichiometric amount of a silyl triflate. Reactions of 1-alkyl-substituted alkenes... 

A series of arylynamides with alkyloxy groups at the ortho position of the aryl group has been prepared by an alkylation/cross-coupling/amidation sequence and a subsequent gold-catalysed reaction provides benzofurans with amine functionalities at the 2-position and alkyl groups at the 3-position. The mechanism of gold(III)-catalysed isomerization of alkyl-substituted allenes to conjugated dienes in the presence of a... 

Metallated 1-ethoxy-1,3-dienes 697 and 712, obtained from the corresponding acetals by means of the LICKOR base, have been treated with alkyl halides, epoxides, carbonyl compounds, carbon dioxide and carboxylic esters affording ( )-l-substituted 1-ethoxy-1,3-dienes and, after hydrolysis, a,P-unsaturated carbonyl compounds1007-1010 (Scheme 186). Intermediates 697 and 712 have been transformed into the corresponding vinyl stan-nanes, which were submitted to Stille couplings with iodobenzene and benzoyl chloride823. 

Substituted, 3d>utadienes. These useful dienes are easily prepared by cross-eoupling of 1,3-butadie[ie-2-ylmagnesium chloride with primary alkyl iodides or bromides catalyzed by Li2CuCl4. Similar coupling is possible with aryl iodides, but yields are lower. 

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