Enantioselective synthetic approaches to cyclopropane and cyclobutane β-amino acids: synthesis and structural study of a conformationally constrained β-dipeptide

Asymmetric Nitrocyclopropanation of α‐Substituted α,β‐Enals Catalyzed by Diphenylprolinol Silyl Ether for the Construction of All‐Carbon Quaternary ­Stereogenic Centers

“…To determine the absolute configuration, we first transformed cyclopropane derivative 9 into known compound 17 and compared its optical rotation with the value in the literature 28. The transformation from 9 to 17 is summarized in Scheme .…”

“…Ethyl ester formation and deprotection afforded protected cyclopropyl amino ester 17 . By comparison of the optical rotation with the literature data,28 the absolute configuration was determined. This absolute configuration, however, did not match that determined by VCD.…”

“…Cyclopropane derivative 17 was therefore synthesized as reported28 starting from the chiral compound, as shown in Scheme . The quaternary chiral center of 17 was constructed by diastereoselective [3+2] cycloaddition of diazomethane, and its diastereofacial selection would be reasonable.…”

A Versatile and Stereoselective Synthesis of Functionalized Cyclobutenes

“…Aiming at biologically relevant scaffolds, the amide derivative 8 smoothly underwent Hofmann rearrangement to give the novel constrained, fully protected cyclobutene-g-amino acid 9. [16] Other manipulations further showcase the synthetic advantage derived from the cyclobutene double bond and hint at potential applications of this method in total synthesis. Thus, ring-opening metathesis/cross-metathesis [17] of azabicycle 11 under an atmosphere of ethylene (1 atm) promoted by Grubbs second-generation catalyst afforded the diastereomerially pure pyrrolidinone 12, whose structure is reminiscent of kainic and domoic acid derivatives.…”

Synthesis of novel β-aminocyclobutanecarboxylic acid derivatives by a solvent-free aza–Michael addition and subsequent ring closure

“…The first cyclobutane-containing dipeptide, which was synthesised by the group of Ortuño starting from cis-β-ACBC 1a, shows a hairpin-like conformation in the solid state, while a cis-cyclobutane-containing β-tetrapeptide and hexaand octamers of trans-β-ACBC 1b fold into 14-and 12-helical conformations resulting from the formation of inter-and intramolecular hydrogen bonds. 13,14,15 Moreover, a β-peptide composed of four cis-β-ACBC 1a residues has shown molecular self-assembly to form nanosized fibrils and gels, 16 and trans,trans-and trans,cis-bis(cyclobutane)-β-dipeptides show a tendency to assemble into nanoscale fibres. 17,18 Another reason for the enhanced interest in carbocyclic β-amino acids is the biological activity of some of these constrained compounds, e.g.…”