Regioselectivity tandem couplings

Fig. 16.22. Palladium-catalyzed C,C coupling with bro-moiodobenzene regioselective tandem coupling I.

Fig. 13.20. Suzuki coupling II for the synthesis of functionalized aromatic compounds regioselective tandem coupling II.

The sulfur function in vinyl sulfides can be displaced in the same manner, using Ni or Pd catalysts, and the methodology has been extended to tandem couplings using l-bromo-2-phenylthioethene (Scheme 17). The regioselectivity of the first step is exactly as that observed with the corresponding p-bromo-vinyl ether (Scheme lb). In just the same way the 1,1-disubstituted alkene (79) can be converted into... 

The first asymmetric procedure consists of the addition of R2Zn to a mixture of aldehyde and enone in the presence of the chiral copper catalyst (Scheme 7.14) [38, 52]. For instance, the tandem addition of Me2Zn and propanal to 2-cyclohexenone in the presence of 1.2 mol% chiral catalyst (S, R, R)-1S gave, after oxidation of the alcohol 51, the diketone 52 in 81% yield and with an ee of 97%. The formation of erythro and threo isomers is due to poor stereocontrol in the aldol step. A variety of trans-2,3-disubstituted cyclohexanones are obtained in this regioselective and enantioselective three-component organozinc reagent coupling. 

The palladium-catalyzed decarboxylative coupling of allyl 2-(benzo[c(jthiazol-2-yl)acetates 118 provides a facile approach to 2-(but-3-enyl)benzo[c(jthiazoles 122 <07JA4138>. The reaction is initiated by nucleophilic attack of Pd(0) on the allyl ester to give Pd-7t-allyl complex 119, which undergoes nucleophilic attack at the less substituted allylic carbon from the benzothiazole nitrogen to produce 120. Decarboxylative dearomatization leads to intermediate 121, and a subsequent aza-Cope rearrangement driven by rearomatization affords the final product 122 and accounts for the unusual regioselectivity. This appears to be the first report of a tandem allylation/aza-Cope reaction driven by decarboxylative dearomatization/ rearomatization. 

A Rh -catalyzed tandem one-pot coupling cycUzation reaction with TMSA and trifluoroacetimidoyl chlorides delivers 2-trifluoromethylated quinolines with good regioselectivity (eq45). i... 

The regioselectivity appeared to be dependent on the electron richness of the starting material. At least an example of tandem H-B addition/Suzuki-Miyaura coupling was explored but it provided the expected product without... 

---