Titanium‐Mediated Oxidative Arylation of Homoallylic Alcohols

Oxidation and Reduction

“…The reaction apparently proceeds through aryltitanation followed by β-hydride elimination; reductive elimination of arene occurred from a Ti(IV)H(aryl) intermediate. 107 A chiral titanium complex with (S,S)-or (R,R)-hydrobenzoin catalysed the enantioselective oxidation of aryl benzyl sulfide by TBHP in n-hexane to give chiral non-racemic and enantiopure aryl benzyl sulfoxides (ee > 98%). It was proposed that the tetrahedral Ti-hydrobenzoin complex was first approached by the sulfide and then by the oxidant to give the octahedral Ti-complex, which was more stable than its counterpart.…”

Carbometallation Reactions

“…Lately, group IV transition metals were reported to promote the oxidative coupling process between alkenes and aromatic organometallic reagents proceeding with an intramolecular carbometallation event. Thus, it was shown that aromatic titanium complexes generated in situ are able to undergo addition to unactivated alkenes such as homoallylic alcohols (Scheme 10.68) [54].…”

“…The intramolecular aryltitanation event then occurs on the proximal alkene moiety to form an oxatitanacycle, which undergoes a reversible β-hydride elimination with the exocyclic hydrogen (H cis ) resulting in mixtures of products. However, in case of extended reaction times or in the presence of an excess of the Grignard reagent, this equilibrium is shifted toward the product of oxidative arylation by the reductive elimination of the arene [54]. Intramolecular carbocyclization reactions of terminal unsaturated alkenylzinc reagents leading to cyclopentylmethylzinc species have been reinvestigated by Cohen [55] and were found to proceed through a radical chain process initiated by traces of oxygen (Scheme 10.71).…”