Rhodium BINAP-catalyzed arylation

Arylmetallic reagents other than arylboronic acid were shown to be applicable in the rhodium-BINAP-catalyzed arylation. Aryltitanium reagent 93 con-... 

Most of the currently applied protocols for rhodium-catalyzed conjugate addition chemistry involve the use of aqueous solvent systems which ensure catalytic turnover by protonation of the intermediate rhodium enolate. Consequently, tandem reaction sequences with electrophiles other than a proton are troublesome. In early investigations, Hayashi reported a rhodium/BINAP-catalyzed conjugate addition-aldol reaction under anhydrous conditions by use of 9-aryl-9-borabicyclo[3.3.1]no nanes (9-Ar-9-BBN) as aryl sources [117]. The reaction between tert-butyl vinyl ketone (145) with 9-(4-fluorophenyl)-9-BBN (146) and propionaldehyde (147) led to the formation of a syn/anti-mixiuve of 148 in a 0.8 to 1 ratio (Scheme 8.39). 

A rhodium(l)-catalyzed system in THF is also effective in the Mizoroki-Heck-type reaction of arylsilanediols with acrylates (Scheme 4).53 Interestingly, the use of aqueous THF switches the reaction to 1,4-addition forming /3-arylated esters. The proposed catalytic cycles for these reactions involve 1,4-addition of an arylrhodium species to an acrylate. The change of the reaction pathway is probably because, in aqueous THF, the resultant Rh enolate 6 undergoes protonolysis rather than /3-elimination. Similar Rh-catalyzed 1,4-additions to a,/3-unsaturated carbonyl compounds have been achieved with arylsilicones,54 arylchlorosilanes,55 and aryltrialkoxysilanes.56,57 The use of a cationic Rh-binap complex leads to highly enantioselective 1,4-additions of alkenyl- and arylsilanes.58 583... 

The Rh-BINAP-catalyzed intramolecular Alder-ene cycloisomerization is very rapid and, therefore, sequentially Rh-catalyzed sequences for the efficient enantioselective generation of five-membered carbo- and heterocycles were envisioned. Korber et al. [21] reported the enantioselective rhodium-catalyzed cycloisomerization of alkyl and (hetero)aryl alkynyl allyl alcohols for the generation of aldehyde-bearing chiral 4-alkyl 3-alkylidene THFs and tetrahydro-furanones, which were converted into a,P-unsaturated carbonyl side chains in a one-pot manner via a concluding Wittig olefination in good yields. 

Addition of Organometallic Reagents to Enones in Aqueous Media Rhodium-catalyzed 1,4-addition of organometallic reagents to a,p-unsaturated compounds was first developed by Miyaura in 1997. Thus, Rh(acac)(CO)2/dppb was found to catalyze the 1,4-addition of aryl- and alkenylboronic acids to several ot,(3-unsaturated ketones in water-containing solvents at 50°C. The reaction conditions were successfully modified for the development of an asymmetric variant of this process by Hayashi and Miyaura in 1998. The important points of modification are (1) the use of Rh(acac)(C2H4)2/(5)-binap as a catalyst and... 

The reaction was efficiently catalyzed by a rhodium complex generated in situ by mixing Rh(acac)(CH2=CH2)2 with 1 equiv of (S)-binap in an aqueous solvent at 100 1C. It was interesting that the enantioselectivity was kept constant at the reaction temperature ranging between 40-120 1C in the addition to 2-cyclohexenone. High enantioselectivity exceeding 90%ee were readily achieved for both cyclic and acyclic a,3-unsaturated ketones with variety of aryl- and alkenylboronic acids. 

Anilides, bearing a sterically demanding orfho-substituent, are known to exist as atropisomers due to a high rotational barrier around aryl-nitrogen single bond. The cationic rhodium(I)/xyl-BINAP complex-catalyzed enantioselective [2+2+2] cycloaddition of 1,6-diynes with trimethylsilylynamides afforded axiaUy chiral anilides with good to excellent enantioselectivity (Scheme 21.21) [25]. 

The rhodium-catalyzed addition of aryl- and 1-alkenylboronic acids tooc, unsaiurated ketones, aldehydes, esters, and amides gave the conjugate 1,4-addition products in high yidds. The ifaodium(I) complexes also catalyzed the 1,2-addition of organoboronic acids to aldehydes or N-sulfonyl aldimines. The dficiency of protocol was demonstrated in the asymmetric addition reactions of organoboronic acids in the presoice of a rhodium(acacV BINAP complex. 

The success of the methodology was extended to other substrates such as a, 3-unsaturated esters and amides by the same group [65]. Enantioselective 1,4-addition of aryltrialkyloxysilanes to the described substrates (Scheme 5.21), catalyzed by a chir2il rhodium complex generated from [Rh(COD)(MeCN)2]2BF,i and (S)-BINAP, was described. Aryl groups can be introduced easily with high enantioselectively at the (3-position of a variety of esters and amides. The enantioselectivity and the chemical yield were affected by the bulkiness of the substituents at the olefin terminal and also by the ester or amide moiety. 

Based on the initial Alder-ene cycloisomerization of alkyl and (hetero)aryl-substituted alkynyl allyl alcohols 13, the rhodium(I)-BINAP complex subsequently can be employed in the reduction of the primary products with hydrogen, furnishing 2,7-dioxabicyclo[3.2.1]octanes 14 in the sense of a sequentially Rh-catalyzed one-pot process (Scheme 12.7) [22]. 

Aryl ethynyl ethers can also be employed in cationic rhodium(I) complex-catalyzed intermolecular [2- -2-1-2] cycloaddition. The [2- -2-1-2] cycloaddition of aryl ethynyl ethers proceeded by using the cationic rhodium(I)/Hg-BINAP catalyst (Scheme 4.13) [24], The same rhodium(I) complex catalyzed cross-[2 - - 2 - - 2] cycloaddition of two molecules of aryl ethynyl ethers with electron-deficient internal alkynes (Scheme 4.14) [24]. 

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