Ti/Pd Bimetallic Systems for the Efficient Allylation of Carbonyl Compounds and Homocoupling Reactions

Abstract

The allylation, crotylation and prenylation of aldehydes and ketones with stable and easily handled allylic carbonates is promoted by a Ti/Pd catalytic system. This Ti/Pd bimetallic system is especially convenient for the allylation of ketones, which are infrequent substrates in other related protocols, and can be carried out intramolecularly to yield five- and six-membered cyclic products with good stereoselectivities. In addition, Ti/Pd-mediated reductions and Würtz-type dimerisation reactions can be readily carried out from allyl carbonates and carboxylates.

Redox‐Neutral α‐Allylation of Amines by Combining Palladium Catalysis and Visible‐Light Photoredox Catalysis

“…2 In contrast, reversal of reactivity of the π‐allylpalladium complex can be realized through two‐electron3 or single‐electron reduction4 (Scheme , paths 2 and 3) in the presence of stoichiometric amounts of reducing reagents (e.g., Et 3 B, Et 2 Zn, InI, SmI 2 , or Mn powder). The resultant allylic metal complex (η 1 ‐type) or allylic radical enables the nucleophilic addition to aldehydes, ketones, and imines,3 as well as radical homocoupling4a,d and intramolecular radical addition reactions 4b–d. Despite the advances, the catalytic generation of an allylic radical from a π‐allylpalladium complex without additional reductants remains a challenge.…”

Allyl Alkyl Carbonates

“…This species fragments further to an allyl radical, which can form the nucleophilic η 3 -allyltitanocene(IV) complex. 18 (F) Alder-ene Reaction 1,4-Dienes can be formed by the Alder-ene reaction of allyl carbonates and alkynes. The E/Z-selectivity could be increased by the use of a permethylated cyclopentadienyl ruthenium complex.…”

New Advances in Titanium-Mediated Free Radical Reactions

“…The titanium/palladium-mediated system has been successfully applied by the same research group for the selective allylation, crotylation and prenylation of aldehydes and ketones [ 59 ] ( Scheme 22 ), for the synthesis of homopropargyl alcohols using propargyl carbonates as pronucleophiles [ 60 ] ( Scheme 23 ), and to promote the intramolecular Michael-type addition of allylic carboxylates to activated alkenes [ 61 ] ( Scheme 24 ). More recently, the efficient allylation of carbonyl compounds starting with allyl carbonates has been performed by replacing Pd with Ni [ 62 ].…”