Stereocontrolled Access to Higher Sugars (Non-1-en-4-ulopyranosyl Derivatives) and Glycomimetics [3-(β-D-Glycopyranosyl)-1-propenes and(3Z)-4,8-Anhydro-nona-1,3-dienitols]

Ring-Closing Olefin Metathesis of 3,3′-(D-Glycopyranosylidene)bis(1-propene) Compounds as a Route to Anomeric Spiro Sugars

“…), it turned out that these conditions produced a mixture of compounds, separable by careful column chromatography and eluted in the following order: 7 , 9 , 12 ,1 then 16 1 (Scheme ). Whereas diene 7 was formed in small amounts, as observed previously,1 the desired compound 9 was obtained in yields not exceeding 40%. Radical‐mediated allylation of 1 was repeated as before, except that the temperature was lowered to approximately ca.…”

“…In a previous paper, we reported on the stereocontrolled synthesis of 3‐(β‐ D ‐glycopyranosyl)‐1‐propenes and on access to unknown D ‐glycopyranosylidenedienes,1 based on free radical reactions applied to anomeric glycosyl dihalides, such as 1 − 3 . It was of interest to consider treatment of these with an excess of allyltributyltin, as a possible route to 3,3′‐( D ‐glycopyranosylidene)bis(1‐propene) derivatives (“ C , C ‐diallyl glycosides”).…”

“…It was of interest to consider treatment of these with an excess of allyltributyltin, as a possible route to 3,3′‐( D ‐glycopyranosylidene)bis(1‐propene) derivatives (“ C , C ‐diallyl glycosides”). Indeed, such compounds had been isolated in trace amounts in the course of our previous investigation 1. Considering that there are only a few scattered synthetically useful routes, based either on free radical2 or on ionic3,4 approaches to C , C ‐disubstituted glycopyranosyl compounds, while access to C , C ‐spirocyclic glycosides5,6 often involves carbene intermediates,7−10 we anticipated that radical‐based allylation of these glycosyl dihalides would be a useful and straightforward method applicable to the synthesis of acetylated 3,3′‐( D ‐glycopyranosylidene)bis(1‐propenes).…”

The synthesis of d-C-mannopyranosides

“…Radical reduction of anomeric carbon-halogen bonds has been reported, but for the most part yields are low and mixtures are obtained (Scheme 59) [204][205][206] An anomeric carbon-nitrogen bond can also be reduced radically. This procedure was shown to be very efficient, giving the b-C-mannopyranoside in both cases (Scheme 60) [207].…”

Furanose-based templates in the chemoselective generation of molecular diversity

“…19 This one-pot transformation involves three widely-known transformations in carbohydrate chemistry, namely: i) the Lemieux, Fraser-Reid electrophilic bromination of glycals, 20 ii) the base-mediated formation of oxiranes from 1,2-halohydrins, 21 and iii) the elimination of anomeric halides mediated by base. 22 Although we have no proof of the actual steps order in the overall transformation, in our opinion, the sequence will likely start with the stereoselective bromination of the electron rich double bond (step i, Scheme 3) to furnish dibromides 9, and since no reaction intermediate (10 or 11) has ever been observed (TLC) in these transformations, a pathway 9-11-4a (involving a reactive allylic bromide) seems more likely. 2.3 Synthesis of epoxy-1'-halo-exo glycal 4b and 4c: Electrophilic halogenation of 4a Access to halo-exo-glycals 4b,c requires just one synthetic operation starting from 4a.…”