Conjugate arylation

Structure 59, which has no conjugating substituents, absorbs in ethanol at 240 nm (log 3.06), with weaker shoulders between 259 and 269 nm. Introduction of one or conjugating aryl groups shifts the... 

Typical examples of n >n UV spectra are illustrated in Tables XIII-XVI. The use of absorption spectroscopy for diagnostic purposes is limited. Thus simple 2//-pyrans, as a rule, show more complex and red-shifted absorption curves in comparison to those of similar 4//-pyrans (Tables XIII and XIV). Analogous spectral behavior for simple 2H- and 4H-thiopyrans is perceptible from Tables XV and XVI. The introduction of conjugating aryl groups and other unsaturated substituents causes a significant overlap of original absorption bands with those of the aromatic systems as well as a bathochromic shift of the longest wave absorption maxima. 

This reaction has been extended to other heteroarene carboxylates and to cycloalk-enones,leadingto conjugated aryl or heteroaryl enones ingood yields (Scheme 10.59).91... 

Another type of intramolecular electrophilic substitution is shown in Equation (1).25 In this case, the reaction sites are located in different substituents on silicon. This reaction mode is useful for highly diastereoselective alkenylation and phenylation of aminoacetals and hemiaminals.26 Intramolecular conjugative arylation of a-enals bearing an aryldimethylsilyl group is effectively promoted by tetrabutylammonium fluoride (TBAF) (Equation (2)).27,27a... 

A range of polycyclic benzo b furans illustrated below was formed by the CuI/TMEDA mediated coupling reaction of conjugated aryl bromide-alkenyl triflates <07TL7578>, and a similar reaction was also found in the synthesis of 5-phenyl morphans <07H(71)881>. 

Next, we have a reductive amination the imine is formed (Chapter 14) from the more re-. HB aliphatic ketone rather than from the conjugated aryl ketone and the hydrogenation reduc, -r... 

Figu re 8.6 Chiral diene ligands for the conjugate arylation. 

Figure 8.8 Phosphine ligands for the palladium(II) complexes for conjugate arylation.

Conjugate Arylation with Diphosphine-Palladium(ll) Complexes... 

Figure 8.10 Suitable acceptors for rhodium/diene-catalyzed conjugate arylation.

Conjugate Arylation of Chiral, Racemic o,p-Unsaturated Carbonyl Compounds... 

Based on initial studies by Krause and Alexakis [100], the highly enantioselective synthesis of trans-5-aryl-2-substituted cyclohexanones 119 was accomphshed by the conjugate arylation of racemic 6-substituted cyclohexenones 117 (Scheme 8.29) [101]. Although the first step did not proceed in a diastereoselective maimer, only the thermodynamically more stable trans-disubstituted cyclohexanone 119 was obtained after epimerization with NaOEt. 

Rhodium-Catalyzed Enantioselective Conjugate Arylation-Protonation... 

Scheme 8.39 Rhodium-catalyzed conjugate arylation-aldol cyclization.

Rhodium-Catalyzed Conjugate Arylation-Aldol-Addition... 

The methodology was extended to the desymmetrization of triones 151 (Scheme 8.41) [119], and diastereo- and enantioselective conjugate arylation/aldol cycliza-tion led to the formation of five- and srx-membered diquinane and hydroquinane structures 152 containing four contiguous stereocenters. 

Feringa recently reported a highly enantio- and diastereoselective one-pot conjugate arylation/allylation sequence (Scheme 8.42) [120] where the initial rhodium/ phosphoramidite-catalyzed conjugate addition of arylboronic acids in dioxane/ water was complemented by a Barbier-type indium-mediated allylation. 

Scheme 8.42 Rhodium-catalyzed conjugate arylation-allylation.

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