Design and application of diimine-based copper(i) complexes in photoredox catalysis.

Structurally different bis(imino)copper(i) complexes were prepared in a highly modular manner and utilized as copper-based photocatalysts in the ATRA reactions of styrenes and alkyl halides. The new photocatalysts showed good catalytic activity and ensured efficient chemical transformations.

Addition of carbon-based nucleophiles to Fmoc-protected acyl iminium ions.

Weakly basic carbon nucleophiles add efficiently to a Fmoc-protected N,O-acetal compound. The new reactions highlight the compatibility of the Fmoc protecting group with moderately basic reaction conditions and should serve as a model for the development of more efficient syntheses of Fmoc-protected amino acids.

A rapid 1H NMR assay for enantiomeric excess of alpha-substituted aldehydes.

In situ derivatization of a variety of alpha-substituted aldehydes via reaction with chiral amines allows convenient and efficient determination of enantiomeric excess. (1)H NMR analysis of the imine diastereomer ratio can be conducted immediately after the aldehyde and amine have been mixed. The results correlate well with ee values determined by more traditional (and slower) methods. This approach may be broadly applicable to alpha-substituted aldehydes. [reaction: see text]

Synthesis of 4,4-disubstituted 2-aminocyclopentanecarboxylic acid derivatives and their incorporation into 12-helical beta-peptides.

An enantioselective synthetic route is reported for trans-2-aminocyclopentanecarboxylic acids (ACPC) bearing geminal side chain pairs at the 4-position. Beta-peptides containing the 4,4-disubstituted ACPC residues adopt the 12-helical conformation, as demonstrated by 2D NMR analysis in aqueous solution. These 4,4-disubstituted ACPC residues display functional groups, including acidic and hydrogen bond donating groups, in a geometrically defined fashion, which should be useful for the design of beta-peptides for specific applications. [structure: see text]

Activation of Fmoc-protected N,O-acetals using trimethylsilyl halides: mechanistic and synthetic studies.

Trimethylsilyl halide activation of Fmoc-protected N,O-acetals yields reactive intermediates capable of efficiently adding to a variety of enamines. NMR studies have provided evidence that a stable halomethyl carbamate intermediate forms in solution. Good yields are obtained over a broad range of enamine nucleophiles encompassing both cyclic and acyclic ketone-derived and aldehyde-derived enamines. Preliminary studies suggest that the enamine additions occur through a concerted, S(N)2-type mechanism.

Enantioselective organocatalytic Michael additions of aldehydes to enones with imidazolidinones: cocatalyst effects and evidence for an enamine intermediate.

An enantioselective intermolecular Michael addition of aldehydes to enones catalyzed by imidazolidinones has been achieved. Chemoselectivity (Michael addition vs aldol) can be controlled through judicious choice of hydrogen-bond-donating cocatalysts. The optimal imidazolidinone/hydrogen-bond-donor pair affords Michael addition products in excess of 90% ee. Furthermore, we have isolated and characterized an enamine intermediate and demonstrated its efficacy as a nucleophile in the observed Michael addition reactions.