Protected -Aldol Compounds from Direct, Catalytic, and Enantioselective Reactions of -Acyl-1,3-oxazinane-2-thiones with Aromatic Acetals.

A direct and asymmetric -aldol reaction of -acyl-1,3-oxazinane-2-thiones with dialkyl acetals from aromatic acetals in the presence of 2-5 mol % [DTBM-SEGPHOS]NiCl, TMSOTf, and lutidine has been developed. It has been established that the oxazinanethione heterocycle, used for the first time as a scaffold in asymmetric carbon-carbon bond-forming reactions, can be smoothly removed to give access to a variety of enantiomerically pure compounds with high synthetic value.

Optimized Asymmetric Synthesis of Umuravumbolide.

Herein, the asymmetric synthesis of umuravumbolide () is described. The new approach features highly stereoselective transformations (dr ≥ 95:5) to install both stereocenters and the olefin, which involve a new radical alkylation, an Ando olefination, and a Krische allylation on a allylic alcohol, not reported before. The application of such successful reactions, together with the limited use of protecting groups and concession steps, makes it possible to complete the synthesis in 10 steps, resulting in a 39% overall yield from chiral -acyl oxazolidinone .

Direct and Asymmetric Aldol Reactions of N-Azidoacetyl-1,3-thiazolidine-2-thione Catalyzed by Chiral Nickel(II) Complexes. A New Approach to the Synthesis of β-Hydroxy-α-Amino Acids.

A direct and asymmetric triisopropylsilyltrifluoromethanesulfonate (TIPSOTf) mediated aldol reaction of N-azidoacetyl-1,3-thiazolidine-2-thione with aromatic aldehydes catalyzed by a chiral nickel(II)-Tol-BINAP complex has been developed (BINAP=2,2'-bis(diphenylphosphino)-1,1'-binaphthyl). The catalytic protocol gives the corresponding anti α-azido-β-silyloxy adducts with outstanding stereocontrol and in high yields. Theoretical calculations account for the stereochemical outcome of the reaction and lay the foundations for a mechanistic model.

Stereoselective Alkylation of Chiral Titanium(IV) Enolates with -Butyl Peresters.

Here, we present a new stereoselective alkylation of titanium(IV) enolates of chiral -acyl oxazolidinones with -butyl peresters from Cα-branched aliphatic carboxylic acids, which proceeds through the decarboxylation of the peresters and the subsequent formation of alkyl radicals to produce the alkylated adducts with an excellent diastereoselectivity. Theoretical calculations account for the observed reactivity and the outstanding stereocontrol. Importantly, the resultant compounds can be easily converted into ligands for asymmetric and catalytic transformations.