Carbohydrate-derived amino-alcohol ligands for asymmetric alkynylation of aldehydes

Highly enantioselective alkynylation of aldehydes catalyzed by a new oxazolidine-titanium complex

The readily available and inexpensive new chiral oxazolidine in combination with Ti(O(i)Pr)(4) was found to catalyze the reaction of an alkynylzinc reagent with various types of aldehydes to generate chiral propargylic alcohols with high enantioselectivities (up to 95%) and excellent yields (up to 98%).

Carbohydrates as Synthetic Tools in Organic Chemistry

While amino acids, terpenes and alkaloids have found broad application as tools in stereoselective organic synthesis, carbohydrates have only lately been recognised as versatile starting materials for chiral auxiliaries, reagents, ligands and organocatalysts. The structural diversity of carbohydrates and the high density of functional groups offer a wide variety of opportunities for derivatization and tailoring of synthetic tools to a specific problem.

Dimethylzinc-Mediated, Enantioselective Synthesis of Propargylic Amines

A one-pot, enantioselective synthesis of N-aryl propargylic amines, using alkynylation reagents obtained from dimethylzinc and terminal acetylenes in combination with various aldehydes and o-methoxyaniline as starting materials, has been developed. Enantiopure beta-amino alcohols derived from norephedrine were used as non-covalent chiral auxiliaries, both in stoichiometric or substoichiometric amount. After optimization, propargylic amines were obtained in good to high yields (up to 93%) and with moderate to high enantiomeric excesses (up to 97% ee). The possibility to recover the chiral auxiliary after the reaction was demonstrated.

Asymmetric addition of 1-ethynylcyclohexene to both aromatic and heteroaromatic ketones catalyzed by a chiral Schiff base-zinc complex

The evaluation of a chiral Schiff base ligand in the zinc-catalyzed asymmetric addition of 1-ethynylcyclohexene to both aromatic and heteroaromatic ketones is reported (with up to 83% enantioselectivity and up to 88% isolated yield).

Ligand accelerated indium(iii)-catalyzed asymmetric alkynylation of aldehydes with 2-methyl-3-butyn-2-ol as an ethyne equivalent donor

Indium(III)-catalyzed asymmetric alkynylation of aryl, heteroaryl, alkyl and alkenyl aldehydes with 2-methyl-3-butyn-2-ol as an ethyne equivalent donor was realized, and products were obtained in moderate to good yields (up to 97%) and high enantioselectivities (up to 99% ee) using 2-10 mol% of catalyst.

Low Ligand Loading, Highly Enantioselective Addition of Phenylacetylene to Aromatic Ketones Catalyzed by Schiff-Base Amino Alcohols

[reaction: see text] Schiff-base amino alcohols 7a,b derived from L-phenylglycine through three simple steps are found to be highly effective for the enantioselective addition of phenylacetylene to aromatic ketones. When the loading of 7b was 1 mol %, an ee value of up to 95% was obtained. However, when 7b was lowered to 0.1 mol %, a high ee value of 85% was still achieved. A practical solution to synthesize the optically active tertiary propargylic alcohols was described.