Stereoselective C-Glycosidations with Achiral and Enantioenriched Allenylsilanes

Abstract

Allenylsilanes are used as carbon nucleophiles in highly stereoselective Lewis acid-promoted C-glycosidations, resulting in the introduction of an internal alkyne with an adjacent stereocenter. Both achiral and chiral allenylsilanes form the desired products with high diastereoselectivity, where the nucleophile adds exclusively to the α-face of the intermediate oxonium ion. Reactions with glucal and galactal afford dihydropyran products, while reactions with a ribose derivative yield dihydrofuran products.

Recent Developments in the Ferrier Rearrangement

“…Allenylsilanes are an important class of carbon nucleophiles in the production of functionalized alkynes 185. Brawn and Panek reported that allenylsilanes underwent stereoselective (>20:1) α‐ C ‐glycosylation with tri‐ O ‐acetyl‐ D ‐glucal ( 5 ) or D ‐galactal ( 4 ) in the presence of TMSOTf, to afford unsaturated α‐ C ‐propargyl glycosides in moderate to high yields 186…”

Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

“…[31] Like their alkene variants, these allenes are good carbon nucleophiles, and add to carbonyl compounds as well as iminum and oxonium ions with stereospecific formation of functionalized alkynes. [32][33][34] Homopropargylic ethers, sulfonamides, and dihydrofurans are synthesized in a highly syn manner. Chiral allenylsilane 22 react diastereoselectively with aldehydes and silyl ethers to give syn-homopropargylic ethers 23, or with aldehydes and sulfonamides to give syn-homopropargylic amines 24. syn-Homopropargylic ethers 23 then undergo thermally induced 1,3-dipolar cycloaddition reactions with an azide moiety or another azide compound to form fused 1,2,3-triazole ring systems 26 and 27.…”

Propargyl Claisen rearrangement: allene synthesis and beyond

“…31,32 It is worth mentioning that the key formation of the allenylsilanes was performed in refluxing xylenes with a catalytic amount of propionic acid on a 25 mmol scale. (R)-24 afforded (S a )-25 in 79% yield and 98% ee while (S)-24 afforded (R a )-25 in 81% yield and 98% ee.…”