Interrupted Pummerer Reaction in Latent/Active Glycosylation

Abstract

A latent/active glycosylation strategy is efficient for rapid ­assembly of oligosaccharides. We recently developed novel OPTB/OPSB and SPTB/SPSB glycosides as two pairs of latent/active glycosyl donors. The active OPSB and SPSB glycosyl donors are efficiently activated by Tf2O via an interrupted Pummerer reaction mechanism. In this account, the design, developments, mechanism studies and applications of these new glycosylation methodologies are described.1 Introduction2 Conceiving Ideas3 Synthesis of OPSB and SPSB Glycosides4 Substrate Scope5 Application in the Synthesis of Natural Products6 Conclusion

Recyclable fluorous-tag assisted two-directional oligosaccharide synthesis enabled by interrupted Pummerer reaction mediated glycosylation

“…1B). [24][25][26][27] In view of these advantages, we envisioned that the installation of uorous side chains on anomeric OPTB and OPSB functionalities (OPTB F and OPSB F respectively) would further facilitate the reducing end to non-reducing end assembly sequence by virtue of the PTFE assisted ltration technology. Most importantly, the uorous tagged anomeric leaving group would be amenable to be cleaved and recovered by IPRm glycosylation and thus allow the non-reducing end to reducing end assembly and overall, provide a two-directional oligosaccharide synthesis (Fig.…”

Alkylation Reactions with Alkylsulfonium Salts

“…Although a series of reviews have highlighted transformations of sulfoniums as cross-coupling partners or intermediates to form valuable compounds, the use of alkylsulfonium salts as alkyl-transfer reagents via C–S bond cleavage has not yet been systematically summarized in the literature. 1c , 5` c d e f g h i j k l , 8…”

Synthesis of N-Alkylpyridin-4-ones and Thiazolo[3,2-a]pyridin-5-ones through Pummerer-Type Reactions

“…Pyridones are an important class of heterocyclic compounds. − For example, a number of N -alkylpyridin-4-one or thiazolo­[3,2- a ]­pyridin-5-one structures were reported to have interesting pharmaceutical activities. − For the synthesis of N -alkylpyridin-4-one, alkylation of the parent 4-pyridone, or its tautomeric form 4-hydroxypyridine, would afford a mixture of N-/O-alkylation products, − namely, the N-alkylated 4-pyridones or 4-alkoxypyridines. Thus, traditional approach to N-alkylated 4-pyridones usually involves the condensation between pyran-4-one and amines, , oxidation of piperidin-4-one, alkylation of pyridin-4-one, − as well as other cyclization reactions. − On the other hand, reports on the synthesis of thiazolo­[3,2- a ]­pyridin-5-one structures almost always involve the cyclization reactions to construct the pyridone rings. − As part of our research program − on the reactivity of activated sulfoxides, − we herein report an alternative Pummerer-type reaction approach to access either N -alkylpyridin-4-one or thiazolo­[3,2- a ]­pyridin-5-one structures from readily available pyridine derivatives …”