Reduction of amine N-oxides by diboron reagents.

Facile reduction of alkylamino-, anilino-, and pyridyl-N-oxides can be achieved via the use of diboron reagents, predominantly bis(pinacolato)- and in some cases bis(catecholato)diboron [(pinB)(2) and (catB)(2), respectively]. Reductions occur upon simply mixing the amine N-oxide and the diboron reagent in a suitable solvent, at a suitable temperature. Extremely fast reductions of alkylamino- and anilino-N-oxides occur, whereas pyridyl-N-oxides undergo slower reduction. The reaction is tolerant of a variety of functionalities such as hydroxyl, thiol, and cyano groups, as well as halogens. Notably, a sensitive nucleoside N-oxide has also been reduced efficiently. The different rates with which alkylamino- and pyridyl-N-oxides are reduced has been used to perform stepwise reduction of the N,N'-dioxide of (S)-(-)-nicotine. Because it was observed that (pinB)(2) was unaffected by the water of hydration in amine oxides, the feasibility of using water as solvent was evaluated. These reactions also proceeded exceptionally well, giving high product yields. In constrast to the reactions with (pinB)(2), triethylborane reduced alkylamino-N-oxides, but pyridine N-oxide did not undergo efficient reduction even at elevated temperature. Finally, the mechanism of the reductive process by (pinB)(2) has been probed by (1)H and (11)B NMR.

Synthesis of sugar-derived spiroaminals via lactamization and metathesis reactions.

A series of sugar-derived spiroaminals has been synthesized by utilizing cross metathesis, ring closing metathesis and lactamization reactions as key steps from 1-C-alkylated glycosyl azides and important correlations in the spectral data between spiroaminals and their respective anomers are reported.

Synthesis of (-)-deoxoprosophylline, (+)-2-epi-deoxoprosopinine, and (2R,3R)- and (2R,3S)-3-hydroxypipecolic acids from D-glycals.

New syntheses of (-)-deoxoprosophylline, (+)-2-epi-deoxoprosopinine, and (2R,3R)- and (2R,3S)-3-hydroxypipecolic acids are reported. Utilization of the chiral functionalities of Perlin aldehydes, derived from 3,4,6-tri-O-benzyl glycals, has been done along with chemoselective saturation of olefins and reductive aminations as key steps.

Mild and efficient chemoselective deprotection of anomeric O-methyl glycosides with trityl tetrafluoroborate.

A facile chemoselective deprotection of anomeric O-methyl glycosides has been achieved in good to excellent yields within 10-40 min with use of trityl tetrafluoroborate in dichloromethane at ambient temperatures. The present method is easily implemented and tolerates different functional groups.

The Dual Role of 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) in the Synthesis of Terminal Aryl- and Styryl-Acetylenes via Umpolung Reactivity.

The dual role of the bicyclic amidine base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was demonstrated in a synthesis of terminal aryl- and styryl-acetylenes. Mechanistically, a tandem process involving elimination/Umpolung/protonation occurs in a single step to generate terminal aryl- and styryl-acetylenes from geminal dibromoalkenes. The key to the success of this transformation lies in the organobase-mediated generation of the acetylide from the 1-bromoalkynes at room temperature. The unique characteristics of DBU as an inherently safer reagent make it an attractive alternative to previous systems wherein required pyrophoric reagents and nonambient temperatures remain unsolved issues. The procedure does not work for the synthesis of alkyl-acetylenes.

Synthesis of fused pyran-carbahexopyranoses as glycosidase inhibitors.

Synthesis of polyhydroxylated oxabicyclo[4,4,0]decanes, which constitute a new family of annulated carbasugars, has been accomplished in a stereoselective manner by employing readily available 1,2-anhydro-3,4,6-tri-O-benzyl-alpha-d-glycopyranoses.