Reagent-Controlled Transition-Metal-Catalyzed Radical Reactions

Easy Access to a Cyclic Key Intermediate for the Synthesis of Trisporic Acids and Related Compounds

“…To achieve the access towards intermediate II, a synthetic sequence of ten steps (Scheme 3) was realized, in which the key step is a stereoselective cyclization mediated by Cp 2 Ti III Cl [36] by means of the homolytic opening of the highly functionalized epoxypolyprene (8, III in Scheme 2) [37][38][39][40]. In this regard the preparation of 8 (or III) in good yield constitutes a useful synthetic novelty which could facilitate the synthesis of either trisporoids or labdanes.…”

“…The catalytic cyclization reaction can be settled through the intermediates described in Scheme 3. The transformation begins with the formation of a Lewis acidbase complex between the oxirane group of 8 and Cp 2 TiCl [37,52], the reagent equivalent of Ti(III). This complex promotes the homolytic opening of the epoxide via one-electron-transfer from the Ti(III) atom, resulting in the formation of the carbonated acyclic β-titanoxy-radical V. V evolves by cyclizing via radical attack at the Δ 2,3 double bond, through a 6-endo-trig process favored by the electronic structure of the tri-substituted double bond, leading to the more substituted radical VI.…”

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

“…A simple solution to minimise heterocoupling processes between the allyl radical and [Cp 2 TiCl] is to decrease the concentration of [Cp 2 TiCl] below the concentration of the Pd catalyst. New developments in titanoceneA C H T U N G T R E N N U N G (III)-regenerating agents [26] allow reactions to be performed with [Cp 2 TiCl 2 ] (5-40 mol %) as a pre-catalyst. [27] Especially, the combination of 2,4,6-collidine and trimethylsilyl chloride (TMSCl), developed in our lab, has proven to regenerate different titanium species (titanium alkoxides, carboxylates or hydrides).…”

Trifluoroacetic acid: a unique solvent for atom transfer radical cyclization reactions

“…[1][2][3][4][5][6][7][8][9] Cyclization 10 of α-carbonyl radicals leading to the formations of lactones, lactams, and cycloalkanones has received considerable attention because of its great potential in natural product synthesis. Several methods have been developed to carry out these transformations, including the tin hydride method, the halogen atom transfer method with bis(tributyltin) or triethylborane, and the organomercurial method.…”