General and Scalable Synthesis of 2-Aryl and 2-Alkyl Pyrimidines via an Electronically Tuned SNAr Approach.

An efficient SNAr approach for generating a wide array of 2-aryl and 2-alkyl pyrimidines in good to high yields was developed. This methodology does not require precious metal catalysts and is compatible with aryl, heteroaryl, and alkyl magnesium halides as nucleophiles. This process is scalable and performed at room temperature well below the temperature of the competing decomposition of the activated 2-tert-butyl sulfonyl pyrimidine electrophile.

Site-selective redox isomerizations of furanosides using a combined arylboronic acid/photoredox catalyst system.

In the presence of an arylboronic acid and a hydrogen atom transfer mediator under photoredox conditions, furanoside derivatives undergo site-selective redox isomerizations to 2-keto-3-deoxyfuranosides. Experimental evidence and computational modeling suggest that the transformation takes place by abstraction of the hydrogen atom from the 2-position of the furanoside-derived arylboronic ester, followed by C3-O bond cleavage via spin-center shift. This mechanism is reminiscent of the currently accepted pathway for the formation of 3'-ketodeoxynucleotides by ribonucleotide reductase enzymes.

Site-Selective and Stereoselective C-H Alkylations of Carbohydrates via Combined Diarylborinic Acid and Photoredox Catalysis.

Diphenylborinic acid serves as a cocatalyst for site- and stereoselective C-H alkylation reactions of carbohydrates under photoredox conditions using quinuclidine as the hydrogen atom transfer mediator. Products arising from selective abstraction of the equatorial hydrogens of cis-1,2-diol moieties, followed by C-C bond formation with net retention of configuration, are obtained. Computational modeling supports a mechanism involving formation of a tetracoordinate borinic ester, which accelerates hydrogen atom transfer with the quinuclidine-derived radical cation through polarity-matching and/or ion-pairing effects.

P-Stereogenic ß-Aminophosphines: Preparation and Applications in Enantioselective Organocatalysis.

The synthesis of stereodefined ß-aminophosphines having both carbon- and phosphorus-based chirality centers is described. The method involves resolution of a mixture of ß-aminophosphine oxide diastereomers accessed by ring-opening of an amino alcohol-derived cyclic sulfamidate. A stereospecific, borane-promoted reduction of ß-aminophosphine oxides, which occurs under mild conditions and with inversion of configuration at phosphorus, is a key step in this process. The products obtained are new building blocks for the synthesis of P-chiral ligands and organocatalysts. In a proof-of-concept application in organocatalysis, the diastereomeric P-chiral ß-aminophosphine-based bifunctional thioureas displayed significantly different activities in the Morita-Baylis-Hillman reaction of methyl acrylate with benzaldehyde derivatives.

A versatile synthesis of chiral ß-aminophosphines.

A method for the preparation of chiral ß-aminophosphines having substituted P-aryl groups is described. Ring-opening of cyclic sulfamidates with metal diarylphosphinites yields ß-aminophosphine oxides, which are then reduced to the corresponding phosphines. Effects of the diarylphosphinite countercation on the regioselectivity of the ring-opening reaction (P- versus O-alkylation) are discussed. This method enables the introduction of electron-deficient, electron-rich and sterically hindered diarylphosphino groups, as demonstrated by the synthesis of a series of novel, P-aryl-substituted ß-aminophosphines derived from tert-leucinol, valinol and phenylglycinol. Access to these derivatives will create new opportunities for steric and electronic tuning of ß-aminophosphine-derived chiral ligands and organocatalysts.