Synthesis of Furanosyl C‐1 Glycals through Palladium‐Catalyzed Reactions of a Furanosyl 2,3‐Anhydro‐exo‐glycal

Abstract

A furanose‐derived 2,3‐anhydro‐exo‐glycal, readily available from D‐mannose in four steps, has proven to be a useful substrate in the preparation of a variety of highly functionalized C‐1 glycals. Upon treatment with Pd0 it affords a π‐allyl palladium complex that can react with nucleophiles such as amines, ethyl malonate, or vinylstannanes. On the other hand, umpolung of the π‐allyl palladium complex with Et2Zn facilitates its reaction with electrophilic aldehydes and ketones.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

1‐exo‐Alkylidene‐2,3‐anhydrofuranoses: Valuable Synthons in the Preparation of Furanose‐Based Templates

“…Compound 1a is able to react smoothly (through the π-allyl palladium complex 36, [27] Scheme 6) with nucleophiles, [11] vinylstannanes [27,28] or, after treatment with ZnEt 2 , with electrophiles [29] to give highly functionalized C-1 glycals [27,30] such as 37-39.…”

Sonogashira Couplings of Halo‐ and Epoxy‐Halo‐exo‐Glycals: Concise Entry to Carbohydrate‐Derived Enynes

“…Because the Sonogashira cross‐coupling reaction takes place at room temperature rather than at 60 °C (and because no appreciable nucleophilic opening of epoxide 8b with amines had been observed at room temperature) a different reaction course could be anticipated for the transformation proposed in Scheme b. Accordingly, we had envisaged that compound 8b would first undergo Sonogashira cross‐coupling at the alkenyl bromide followed by generation of a π–allyl palladium complex (e.g., 29 ),52 which could then react with the amine (NHR 1 R 2 ) to give functionalized enynes, for example, 30 (Scheme b).…”

Furanose-based templates in the chemoselective generation of molecular diversity

“…34,35 With that in mind, we studied the reaction of 4a with Pd(0) in the presence of nucleophiles (4a-A), 19b electrophiles (4a-B), 36 and vinyl stannanes (4a-C) 37 as shown in Scheme 9. nucleophiles and amines, to give substituted allylic alcohols, e.g., A (Scheme 9). In order to test this transformation, we first treated vinyloxirane 4a with Pd(OAc) 2 and PPh 3 in THF at rt, overnight, in the presence of methyl malonate.…”

“…In keeping with literature precedents, compound 35, generated by 1,2-addition was obtained as the minor isomer (1.4:1 ratio). 37 The structural assignments were based on the study of their 1 H-and 13 C NMR spectra, and the configuration at C-2 in compound 35, already inferred by mechanistic reasons, was confirmed by a NOESY experiment that showed the correlation of H-3 with the non-terminal vinylic proton.…”