Completely Stereocontrolled Aldol Reaction of Chiral β-Amino Acids

Abstract

A general protocol to independently access stereoisomerically pure β'-hydroxy-β-amino acid derivatives that is based on dibutylboron triflate-mediated aldol reaction of suitably protected β-amino acids bearing chiral oxazolidinone auxiliary is reported. The method smoothly afforded syn-aldol (α,β'-syn) products in pure form and excellent isolated yield. Both α,β-syn and α,β-anti isomers are readily accessible solely through the choice of the oxazolidinone chirality. This method allows for the preparation of stereoisomeric β'-hydroxy-β-amino acid derivatives that were previously unreported.

Chemoenzymatic Hydroxymethylation of Carboxylic Acids by Tandem Stereodivergent Biocatalytic Aldol Reaction and Chemical Decarboxylation

“…Enantiomerically pure 2-substituted 3-hydroxycarboxylate esters are an important class of chiral building blocks widely used in organic synthesis. − For example, ( S )- and ( R )-methyl 3-hydroxy-2-methylpropanoate (i.e., Roche esters) are largely employed as precursors for the preparation of bioactive natural compounds and pharmaceuticals (e.g., discodermolide with potent antimitotic activity, epothilone analogue ZK-Epo (sagopilone), the ionophore antibiotic zincophorin, cytotoxic marine natural products auripyrones A and B, the depsipeptide stevastelin B3, and the antifungal polyketide soraphen A). − Other chiral 2-substituted 3-hydroxycarboxylate esters can be found in the preparation of peptide deformylase inhibitors (Figure ). , …”

1H−15N HMBC NMR as a tool for rapid identification of isomeric azaindoles: The case of 5F‐MDMB‐P7AICA

“…In addition, the nitrogen chemical shifts are highly sensitive to structural changes, more so than proton and carbon chemical shifts. Although the low natural abundance of 15 N (0.37%) and gyromagnetic ratio (−2.713 × 10 7 rad T −1 s −1 ) make direct observation of the 15 N nuclide difficult, this has been circumvented by inverse‐detected long‐range heteronuclear shift correlation techniques that are nowadays a part of standard NMR instrumental setup and require relatively small amounts of samples and experimental time . For this investigation the 15 N chemical shifts were extracted from standard 1 H– 15 N HMBC spectra with the parameters adjusted for a long‐range 1 H– 15 N coupling constant of 5 Hz.…”

Advances and mechanistic insight on the catalytic Mitsunobu reaction using recyclable azo reagents

“…7 , suggest carbonimidate structural fragments as they are consistent with the 15 N NMR data of dimethyl cyclohexylcarbonimidate ( 50 in Scheme 1 , δ N 181 ppm). 32 Although this is reminiscent of a five-membered oxadiazophosphole ring structure ( e.g. , O , N -phosphorane 52 in Scheme 1 ), the 31 P NMR chemical shift of such an intermediate should possess a negative value.…”