2-Pyridylsulfone- and fluoroalkylated group-activated olefins underwent highly efficient diastereo- and enantioselective 1,3-dipolar cycloadditions across various aromatic and aliphatic nitrones in the presence of a chiral Ni /bis(oxazoline) catalyst. The process was tuned by 4 Å molecular sieves, chiral bis(oxazoline) ligands, reaction solvents, and temperature. A wide array of optically pure fluoroalkylated isoxazolidines were obtained, thus facilitating the asymmetric synthesis of an enantioenriched α-trifluoromethylated γ-amino alcohol in gram-scale and a trifluoromethylated derivative of 1,3-oxazinan-2-one with potential pharmaceutical interest. A stereochemical model, based on the absolute configuration of one adduct and some control experiments, was postulated to account for the observed endo- and enantioselectivity.

The 1,3‐dipolar cycloadditions of β‐fluoroalkyl vinylsulfones and nitrile oxides to deliver 5‐fluoroalkyl‐3‐substituted 2‐isoxazolines has been established under mild conditions in up to 85% yield with excellent regio‐ and diastereoselectivities (all d.r. >99 : 1), and thus facilitated rapid access to 5‐fluoroalkyl‐3‐Ph‐2‐isoxazoles by DBU‐mediated elimination of the pyridyl sulfone group.

2-Pyridylsulfone-and fluoroalkylated group-activated olefins underwent highly efficient diastereo-and enantioselective 1,3-dipolar cycloadditions across various aromatic and aliphatic nitrones in the presence of ac hiral Ni II / bis(oxazoline) catalyst. The process was tuned by 4 molecular sieves,chiral bis(oxazoline) ligands,reaction solvents,and temperature.Awide arrayo fo ptically pure fluoroalkylated isoxazolidines were obtained, thus facilitating the asymmetric synthesis of an enantioenriched a-trifluoromethylated g-amino alcohol in gram-scale and at rifluoromethylated derivative of 1,3-oxazinan-2-one with potential pharmaceutical interest. A stereochemical model, based on the absolute configuration of one adduct and some control experiments,w as postulated to account for the observed endo-and enantioselectivity.

A highly atom-economic, regio-and stereospecific synthesis of fluorinated pyrazolidinones and isoxazolidines is disclosed under catalyst-and additive-free mild conditions. The diastereoselectivity with different type of 1,3-dipoles is elucidated by using DFT calculations in CH 3 CN. Furthermore, a reaction using a chiral azomethine imine, a gram-scale synthesis, and a reductive desulfonylation are also presented.

No abstract

The regio‐ and stereoselective 1,3‐dipolar reaction is an important tool to build five‐membered heterocycles. Fluoroalkylated α,β‐unsaturated building blocks were used in the 1,3‐dipolar reaction of nitrones and azomethine imines without any catalysts and additives to obtain fluorinated pyrazolidinones and isoxazolidines. High endo‐selectivity for nitrones and exo‐selectivity for azomethine imines were observed, and supported by DFT calculations of Gibbs free energy changes in CH3CN. More information can be found in the Full Paper by Yi‐Yong Huang et al. on page 1830 in Issue 9, 2018 (DOI: 10.1002/ajoc.201800435).