Synthesis Of Axially Chiral Allenes And Iron-catalyzed Oxidation Reactions Of β-amino Alcohols

Allenes are a class of compounds with a 1,2-diene-based axial chirality when the substituents of each 1- and 3-carbon atoms are different. These compounds play more and more important roles in organic synthesis, pharmaceuticals and material sciences due to their recently developed new reactions. Chemists pay more and more attention to the efficient synthesis of optically active allenes because of possible transfer of axial chirality of allenes to the central chirality in the products.Aldehydes are important starting materials for 1,3-allene synthesis via ATA reaction (allenylation of terminal alkynes). One of the most widely used methods to synthesize aldehydes is the oxidation of the corresponding alcohols. Optically active a-chiral amino aldehydes play important role in organic synthesis. Thus, we studied the oxidation of optically active β-chiral amino alcohols using molecular oxygen as the oxidant.Part I. Synthesis of axially chiral allenes.1. We have developed a procedure for the synthesis of axially chiral aryl-substituted 1,3-allenes from terminal alkynes, aromatic aldehydes, and commercially available chiral amine, i.e. (S)-or (R)-α,α-diphenylprolinol, in moderate yields and up to 96% ee.2. We have developed a new improved simple bimetallic (Zn2+/Cu+) asymmetric approach for non-functionalized axially chiral allenes from non-functionalized terminal alkynes and aldehydes by taking advantage of the readily available and cheap chiral amino alcohol (S)- or (R)-a,a-diphenylprolinol.Part II, Iron-catalyzed oxidation of β-chiral amino alcohols.In this part, we preliminarily studied the oxidation of β-chiral amino alcohols to the corresponding optically active aldehydes using molecular oxygen as the oxidant with a moderate to good yields without racemization.