Recent advances in ring-forming reactions of donor–acceptor cyclopropanes

Donor-acceptor substituted cyclopropane to butanolide and butenolide natural products: enantiospecific first total synthesis of (+)-hydroxyancepsenolide

An oxygen substituted donor-acceptor cyclopropane (DAC) is used as a common intermediate in the enantiospecific collective total synthesis of butanolide- and butenolide-based natural products like (+)-juruenolide C and D, (+)-blastmycinone, (+)-antimycinone, and (+)-ancepsenolide. Enantiospecific first total syntheses of (+)-hydroxyancepsenolide and its acetate are achieved confirming their absolute stereochemistry.

The [4+2] cycloaddition of donor-acceptor cyclobutanes and nitrosoarenes

The Yb(OTf)3 catalyzed [4+2] cycloaddition between donor-acceptor cyclobutanes and nitrosoarenes is disclosed. This method facilitates the synthesis of tetrahydro-1,2-oxazines in good to excellent yields as single diastereomers. Except for a few electron-deficient nitrosoarenes, excellent regioselectivity was observed throughout these studies.

Cyclization and annulation reactions of nitrogen-substituted cyclopropanes and cyclobutanes

This feature article covers recent progress in cyclization and annulation reactions of aminocyclopropanes and aminocyclobutanes to access nitrogen-rich building blocks.

1,3-Carbon D–A strategy for [3 + 2] cycloadditions/annulations with imines: synthesis of functionalized pyrrolidines and related alkaloids

[3 + 2] Cycloaddition/annulation: this article summarize the recent developments in synthesis of pyrrolidines and related alkaloids through complementary [3 + 2] cycloaddition/annulation of 1,3-carbon D–A precursors with imines.

AlCl3-promoted [3 + 2] annulation of cis-2,3-disubstituted cyclopropane 1,1-diesters with isothiocyanates: stereoselective synthesis of densely substituted 2-iminodihydrothiophenes

cis-2,3-Disubstituted cyclopropane 1,1-diesters were found to be much more reactive than their corresponding trans-isomers in the AlCl3-promoted [3 + 2]-annulations with isothiocyanates. The reaction with the cis-cyclopropanes proceeded to completion within minutes, providing a variety of densely substituted diastereomerically pure 2-iminodihydrothiophenes in moderate to excellent yields.

Linear and cyclic hybrids of alternating thiophene-amino acid units: synthesis and effects of chirality on conformation and molecular packing

The dipeptide isostere 5-aminothiophene carboxylic acid has been combined with L-phenylalanine moieties to provide linear and cyclic hybrid oligopeptides. A suitable protecting group strategy and appropriate coupling methods have been developed to guarantee a high degree of enantiopurity of the resulting amides. Cyclic tetraamides have been efficiently obtained by macrocyclization of the linear derivatives. In the case of racemized cyclization precursors, two diastereomeric macrocycles (S,S/R,R and meso) have been isolated. Their crystal structures show clear effects of the stereogenic centers on the ring conformations and molecular packing.