Pd(II)-Catalyzed Enantioselective Ring-Contraction for the Construction of 1,4-Benzoxazines

Enantioselective ring-contraction reactions have not been widely reported. We have developed an enantioselective ring contraction of 5,6-dihydro-2H-benzo[b][1,4]oxazocines, affording enantiomerically enriched 3,4-dihydro-2H-1,4-benzoxazine derivatives as single regioisomers. An acidic additive is necessary in order to obtain the products with good yields and enantiomeric ratios (up to 93% yield, 98:2 er). The reaction was successfully performed on a gram scale, and the products can be derivatized easily.

Lewis acid-catalysed nucleophilic opening of a bicyclic hemiaminal followed by ring contraction: Access to functionalized L-idonojirimycin derivatives

The Lewis acid-catalyzed nucleophilic opening of a D-gluco-configured bicyclic hemiaminal has been examined. Several Lewis acids and silylated nucleophiles have been screened allowing the introduction of acetophenone, phosphonate or nitrile at the pseudoanomeric position in satisfactory yields and high 1,2 trans stereoselectivities. Their skeletal rearrangement triggered by the N-benzyl anchimeric assistance provided the corresponding L-ido-configured piperidines displaying various functional groups at C-6 position in good yield.

Highly efficient [3+3] cycloaddition reactions of in situ generated aza-oxyallyl cation with nitrones

An efficient protocol was developed for the synthesis of 1,2,4-oxadiazinan-5-one derivatives via [3+3] cycloaddition ofin situgenerated aza-oxyallyl cations with nitrones. This method provides high yields of the heterocyclic products, excellent regioselectivity and broad substrate scope.

N–O linkage in carbohydrates and glycoconjugates

The synthesis and chemical and physicochemical properties as well as biological and medical applications of various hydroxylamine-functionalized carbohydrate derivatives are summarized.