Reductive Samariation of Anomeric 2-Pyridyl Sulfones with Catalytic Nickel: An Unexpected Improvement in the Synthesis of 1,2-trans-Diequatorial C-Glycosyl Compounds

✍ Scribed by Nicolas Miquel; Gilles Doisneau; Jean-Marie Beau

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 115 KB
• Volume: 39
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/1521-3773(20001117)39:22<4111::aid-anie4111>3.0.co;2-c

✦ Synopsis

on the occasion of his 62nd birthday A direct method for the synthesis of C-glycosyl compounds derived from neutral hexoses was recently developed by our group. This procedure, which consists in the reductive samariation of anomeric 2-pyridyl sulfones in the presence of carbonyl compounds (Barbier procedure), yields exclusively 1,2-trans C-glycosyl compounds in the hexopyranosyl series, typically the a-C-mannopyranosyl or b-C-glucopyranosyl compounds. [1±3] In the mechanistic rationale formulated earlier, we proposed that the anomeric radical 2, which results from the first electron transfer, is further reduced to a kinetic a-oriented organosamarium 3 which, in the gluco series, either syn-eliminates to glucal 5 or anomerizes to the bspecies 4 (Scheme 1). The latter species does not transeliminate, as it is stable enough at room temperature to react O OP BnO O OP BnO SmI 2 O OP BnO SmI 2 O OP BnO OH R 2 R 1 O R 1 R 2 O BnO O OP SO 2 (2-Py) BnO BnO OBn SmI 2 SmI 2 2 1 3 4 5 6 Scheme 1. Previous mechanistic proposal for the coupling of anomeric 2-pyridyl sulfones with carbonyl compounds mediated by samarium diiodide. 2-Py 2-pyridyl; P protecting group.