Asymmetric hydrogenation for the synthesis of 2-substituted chiral morpholines

Development and Application of SPOSiPs: A Class of Diphosphine Ligands Based on SPOSiOL

Here, we report the development and application of a novel class of spirosilacycle-based diphosphine ligands (SPOSiPs). This type of diphosphine ligand could be readily prepared in two steps with high efficiency starting from enantiopure spirobiphenoxasilin-diol (SPOSiOL). According to the structural analysis of SPOSiP and its PdCl2 complex, SPOSiPs possess a flexible chiral pocket and feature a rigid configuration, a large dihedral angle, a long P-P distance, and a large P-M-P bite angle in their metal complexes. The potentials of SPOSiPs in asymmetric catalysis have also been preliminarily disclosed.

Access to N-α-quaternary chiral morpholines via Cu-catalyzed asymmetric propargylic amination/desymmetrization strategy

Morpholines are widespread in many biologically and catalytically active agents, thus being an important aim of pharmaceutical and synthetic chemists. However, efficient strategies for the catalytic asymmetric synthesis of chiral morpholines bearing crowded stereogenic centers still remain elusive. Herein, we disclose a Cu-catalyzed asymmetric propargylic amination/desymmetrization strategy to help resolve this challenge. As a result, two kinds of structurally various chiral morpholines bearing rich functional groups and N-α-quaternary stereocenters were produced with high efficiency and selectivity (42 examples, up to 91 % yield, 97:3 er and > 19:1 dr). In addition, a series of transformations were performed to demonstrate the synthetic utility of this methodology. In particular, a hit compound for new antitumor drugs was identified through cellular evaluation. Furthermore, mechanistic investigations reveal that, hydrogen bonding in the key copper-allenylidene intermediate together with π-π stacking aids remote enantioinduction.

Organocatalytic Desymmetric Double Aza-Michael Addition Cascade: Enantioselective Synthesis of Fused Morpholines

Double aza-Michael addition (DAM) has become an emerging strategy for the construction of two carbon-nitrogen bonds in a single step, which can significantly simplify the synthesis of N-heterocycles. Hitherto, their asymmetric catalytic genre remains unattempted. Herein, we describe the judicious design of an organocatalytic enantioselective desymmetric double aza-Michael addition cascade to access a series of functionalized fused morpholines with excellent yields and diastereo- and enantioselectivities. A one-pot telescopic synthesis was demonstrated for a bridged triheterocyclic compound. In addition, scale-up synthesis and various attractive postsynthetic modifications of the title products amplify the significance of the current methodology.

Zinc chloride-catalyzed cyclizative 1,2-rearrangement enables facile access to morpholinones bearing aza-quaternary carbons

Morpholines and morpholinones are important building blocks in organic synthesis and pharmacophores in medicinal chemistry, however, C3-disubstituted morpholines/morpholinones are extremely difficult to access. Here we show the ZnCl2-catalyzed cyclizative 1,2-rearrangement for the efficient synthesis of morpholinones bearing aza-quaternary stereocenters. A series of structurally diverse C3-disubstituted morpholin-2-ones which are difficultly accessible by existing methods were efficiently constructed from readily available two achiral linear compounds. Notably, mechanistic studies reveal that this reaction proceeds via an unusual sequence of direct formal [4 + 2] heteroannulation regioselectively delivering specific α-iminium/imine hemiacetals followed by a 1,2-esters or amides shift process, which is different from the reported mechanism of the aza-benzilic ester rearrangements.

Synthesis of Oxazolidines and Dihydroxazines via Cyclization of α-Aminated Ketones

A new approach to oxazolidines and dihydroxazines was developed by regioselective cyclization of α-aminated ketones under transition metal-free conditions. Oxazolidine derivatives were generated in the presence of chloro benziodoxole and TFA, while dihydroxazines were formed without a hypervalent iodine reagent. The reaction was performed under room temperature and gave the products in good to excellent yields.

Azole-Directed Cobalt-Catalyzed Asymmetric Hydrogenation of Alkenes

The azole-directed cobalt-catalyzed asymmetric hydrogenation of alkenes has been developed with high efficiency. With this approach, chiral pyrazole compounds were obtained in quantitative yields and excellent enantioselectivities (up to 99 % ee) under mild conditions, and the hydrogenation was conducted on a gram scale with up to 2000 TON. Several useful applications were demonstrated including the convenient introduction of β-chirality to a drug intermediate containing an azole ring.

Accessing Chiral 2,2-Disubstituted Morpholines via Organocatalytic Enantioselective Chlorocycloetherification

Chiral morpholine is an important scaffold in organic synthesis and a pharmacophore in medicinal chemistry. However, catalytic enantioselective procedure for the construction of morpholine remains sparse. We report herein a...