Nitro-polyols via Pyridine Promoted CC Cleavage of 2‑Nitroglycals. Application to the Synthesis of (−)-Hyacinthacine A1

A mild and convenient transformation for the synthesis of nitro-polyols is described. The nitro-polyol derivatives were prepared either from 2-nitroglycals via a pyridine-promoted scission of the carbon–carbon double bond or from glycals via a sequential nitration–scission procedure. The generated nitro-polyols could undergo a stereoselective Michael addition reaction. The utility of the addition products was exemplified by the concise synthesis of (−)-hyacinthacine A1 and 7a-<i>epi</i>-(−)-hyacinthacine A1

Access to Chiral Tetrahydroquinazolines/1,3-Benzoxazines via Iridium-Catalyzed Asymmetric [4 + 2] Cycloaddition

An iridium-catalyzed asymmetric [4 + 2] cycloaddition of 1,3,5-triazinanes with 2-(1-hydroxyallyl)anilines/2-(1-hydroxyallyl)phenols has been developed, providing a straightforward and efficient approach to a wide range of tetrahydroquinazolines in good yields and excellent enantioselectivities (up to >99% ee). Typically, chiral 1,3-benzoxazines, which are challenging substrates in asymmetric [4 + 2] cycloaddition, could be obtained in excellent enantioselectivities via this protocol

Stereocontrolled Synthesis of 2‑Deoxy‑<i>C</i>‑glycopyranosyl Arenes Using Glycals and Aromatic Amines

An efficient and stereoselective one-pot, two-step tandem α-arylation of glycals from readily available aryl amines via stable diazonium salts has been developed. Moreover, the stereoselective preparation of the challenging β-<i>C</i>-glycosyl arenes by the anomerization of α-<i>C</i>-glycosides using HBF₄ is also described. This protocol has a broad substrate scope and a wide functional-group tolerance. It can be used for the gram-scale preparation of 3-oxo-<i>C</i>-glycosides, which are versatile substrates for the preparation of many biologically important <i>C</i>-glycosides