Highly diastereoselective lithium enolate aldol reactions of butane-2,3-diacetal desymmetrized glycolic acid and deprotection to enantiopure anti-2,3-dihydroxy esters

A lactate-derived chiral aldehyde for determining the enantiopurity of enantioenriched primary amines

In this paper we describe the use of a chiral aldehyde derived from lactate esters for determining the enantiopurity of primary amines, via the formation of diastereomeric imines.

Highly stereocontrolled and regiocontrolled syntheses of 2,3,4-trisubstituted alkanoates and lactones

New chlorodiols (±)-3 and (±)-5 are densely functionalized and versatile synthons. They are converted in one step on a gram scale into 2-chlorolactones (±)-6 and (±)-7 and into 4-hydroxy glycidate esters (±)-9 and (±)-10. The 4-hydroxy glycidate esters (±)-9 and (±)-10 are converted stereospecifically and regiospecifically into oxazolines (±)-13 and (±)-14 and into cyclic carbamates (±)-18-(±)-20. The 4-hydroxy glycidate ester (±)-10 undergoes stereocontrolled and regiocontrolled epoxide opening by sodium azide to form the 2-azido-3,4-dihydroxy alkanoate (±)-21. Finally, chlorodiol (±)-5 reacts stereospecifically with silver triflate to form the 2,3-dihydroxyfuranone (±)-26.

Highly diastereoselective preparation of anti-1,2-diols by catalytic addition of alkynylsilanes to alpha-silyloxyaldehydes

The catalytic, diastereoselective coupling of alpha-silyloxy aldehydes and alkynylsilanes catalyzed by a nickel(0) N-heterocyclic carbene complex provides an effective entry to anti-1,2-diols. The scope of couplings and extent of diastereoselection are excellent across a range of substrates.

A Fascination with 1,2-Diacetals

1,2-Diacetals are readily prepared, rigid structural motifs that provide a wide range of opportunities for applications in natural product assembly. These uses encompass selective 1,2-diol or alpha-hydroxy acid protection, enantiotopic recognition and desymmetrization methods, chiral memory applications, and reactivity control in oligosaccharide synthesis, as well as functioning as templating components, chiral auxiliaries, and building blocks. 1,2-Diacetals are often more stable and lead to products with enhanced crystallinity compared to their five-ring acetonide counterparts. Many 1,2-diacetals have favorable NMR parameters, which facilitate structural assignment, particularly during asymmetric reaction processes.

Michael, Michael-aldol and Michael-Michael reactions of enolate equivalents of butane-2,3-diacetal protected glycolic acid derivatives

Consecutive coupling reactions of butane-2,3-diacetal protected glycolic acid derivatives with Michael acceptors and aldehydes are reported. An enantiopure sample of this building block was used to kinetically resolve a chiral Michael acceptor present as a racemic mixture of enantiomers.

Studies on the generation of enolate anions from butane-2,3-diacetal protected glycolic acid derivatives and subsequent highly diastereoselective coupling reactions with aldehydes and acid chlorides

Highly diastereoselective coupling reactions of enolates derived from butane-2,3-diacetal protected glycolic acids 1 and 2 and their alkylated derivatives with aldehydes are reported together with their efficient acid-catalysed deprotection to yield enantiopure anti-2,3-dihydroxyesters. A procedure to provide the corresponding syn-2,3-dihydroxyesters is also described in two cases, proceeding via an acylation-reduction sequence. An usual double addition reaction of butane-2,3-diacetal protected glycolic acid to small aliphatic acid chlorides provides a synthetically useful, densely-functionalised lactone after acidic deprotection.

Preparation of enantiopure butane-2,3-diacetals of glycolic acid and alkylation reactions leading to α-hydroxyacid and amide derivatives

The preparation of butane-2,3-diacetal protected glycolic acid and related systems is described together with highly selective alkylation reactions of (R,R) and (S,S) butanediacetal protected glycolic acid. These compounds are readily deprotected to give enantiopure alpha-hydroxyacids, alpha-hydroxyesters or alpha-hydroxyamides by suitable choice of conditions.

Highly diastereoselective Michael addition reactions of butane-2,3-diacetal desymmetrized glycolic acid. Preparation of alpha-hydroxy-gamma-amino acid derivatives

[reaction--see text] The butane-2,3-diacetal (BDA) desymmetrized glycolic acid building block undergoes efficient and highly diastereoselective lithium enolate Michael additions to alpha,beta-unsaturated ketones, lactones, and nitro olefins. Subsequent deprotection of these Michael adducts gives alpha-hydroxy acids in very high yield. Hydrogenation of the nitro group in some of the adducts leads to gamma-lactams, which can be easily converted into alpha-hydroxy-gamma-amino acid derivatives.