Aryltitanium reagents

Scheme 2.57 Rhodium-catalyzed enantioselective 1,6-addition of aryltitanium reagents to 3-alkynyl-2-cycloalkenones 180 (ee values referto the corresponding allenic enol pivalates).

A rhodium-catalyzed asymmetric synthesis of chiral titanium enolates by 1,4-addition of aryltitanium reagents to a,p-enones under aprotic conditions has... 

When a,p-unsamrated sulfones are employed as substrates for the rhodium-catalyzed 1,4-addition of aryltitanium reagents, they provide cine-substitution products instead of regular 1,4-addition products [Eq. (3.16)]. This new process... 

Scheme 3.23 Rhodium-catalyzed c/ne-substitution of alkenyl sulfones with aryltitanium reagents [41].

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

In the case of the use of aryltitanium reagents in the rhodium-catalyzed asymmetric 1,4-addition to cyclic and acyclic a, 3-unsaturated enones, only one report was found in literature. Hayashi and coworkers [63] reported a study concerning the use of aryltitanium reagents. The intermediate chiral titanium enolates formed were isolated as silyl enol ethers by way of titanate-type enolates generated by the addition of lithium isopropoxide to the titanium enolates. High enantioselectivities were achieved using (5)-BINAP (Scheme 5.19). 

Scheme 5.19 Rhodium-catalyzed asymmetric 1,4-addition of aryltitanium reagents reported by Hayashi and co orkers [63] - Generation and isolation of silyl enol ethers and derivatives.

Although the enantioselective stoichiometric addition of chiral aryltitanium reagents have been reported in 1987 [66], the catalytic enantioselective aryl addition to carbonyl compounds with titanium catalyst was realized by Walsh using the catalyst prepared from bis(sulfonamide) ligand and Ti(OTr)4 with diarylzinc as the nucleophiles, to afford the tertiary alcohol in good to excellent enantioselectivities for a range of ketone substrates [67]. Very recently, Gau reported that... 

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