Highly Enantioselective Imine Cinnamylation with a Remarkable Diastereochemical Switch

A Regio- and Stereodivergent Synthesis of Homoallylic Amines by a One-Pot Cooperative-Catalysis-Based Allylic Alkylation/Hofmann Rearrangement Strategy

Herein, we report a modular synthetic route to linear and branched homoallylic amines that operates through a sequential one-pot Lewis base/transition-metal catalyzed allylic alkylation/Hofmann rearrangement strategy. This protocol is operationally trivial, proceeds from simple and easily prepared substrates and catalysts, and enables all aspects of regio- and stereoselectivity to be controlled through a conserved experimental protocol. Overall, the high levels of enantio-, regio-, and diastereoselectivity obtained, in concert with the ability to access orthogonally protected or free amines, render this a straightforward and effective approach for the preparation of useful enantioenriched homoallylic amines. We have also demonstrated the utility of the products in the context of pharmaceutical synthesis.

1,2-Amino alcohol-dependent Petasis allylboration for racemic and chiral homoallylamines

Asymmetric Petasis allylboration among an aldehyde, 1,2-amino alcohol and pinacolallylboronate has been established at room temperature without any catalysts.

Asymmetric cinnamylation of N-tert-butanesulfinyl imines with cinnamyl acetates: total syntheses of (+)-lycoricidine and (+)-7-deoxypancratistatin

Highly diastereoselective palladium catalyzed cinnamylation of N-tert-butanesulfinyl imines with cinnamyl acetates has been established to provide enantioenriched β-aryl homoallylic amines. The synthetic application of this stragety has been successfully demonstrated in the concise total syntheses of antitumor natural products (+)-lycoricidine and (+)-7-deoxypancratistatin.

Single or Synergistic Kinetic Resolutions of Chiral Allylalanes: Two Complementary Routes for the Asymmetric Synthesis of Syn Homoallylamines

Two strategies based on kinetic resolution(s) of chiral alanes and providing enantioenriched syn homoallylamines are reported. The first implies a single kinetic resolution of the alane using camphor; the second requires two sequential kinetic resolutions using the synergistic combination of (-)-camphor/(R)-tert-butylsulfinamide-derived imines. This syn selectivity, specific to the use of allyaluminum, opens the way to the preparation of valuable building blocks as illustrated by the synthesis of (+)-epilupinamine.

Regiodivergent and Diastereoselective CuH-Catalyzed Allylation of Imines with Terminal Allenes

A copper-catalyzed, chemoselective hydrometalation process enables the use of simple allenes as allylmetal nucleophile surrogates in imine allylation reactions. By modulating the nitrogen-protecting group, either highly branched- or linear-selective addition can be achieved from the same allene. Both reactions exhibit excellent diastereoselectivity and broad functional-group tolerance. Preliminary results indicate that good enantioselectivity can also be achieved in the linear-selective reaction. Finally, a mechanistic model for the regiodivergence is proposed on the basis of density functional theory calculations.

Copper-catalysed enantioselective stereodivergent synthesis of amino alcohols

The chirality, or ‘handedness’, of a biologically active molecule can alter its physiological properties. For this reason, it is routine procedure in the drug discovery and development process to prepare and fully characterize all possible stereoisomers of a drug candidate for biological evaluation^1,2. Despite many recent advances in asymmetric synthesis, the development of general and practical strategies to obtain all possible stereoisomers of an organic compound bearing multiple contiguous stereocenters remains a significant challenge³. In this manuscript, we report a stereodivergent copper-based approach for the expeditious construction of amino alcohols with high levels of chemo-, regio-, diastereo- and enantioselectivity. Specifically, these amino alcohol products were synthesized using the sequential copper hydride-catalyzed hydrosilylation and hydroamination of readily available enals and enones. This strategy provides a route to all possible stereoisomers of the amino alcohol products, which contain up to three contiguous stereocenters. Catalyst control and stereospecificity were simultaneously leveraged to attain exceptional control of the product stereochemistry. Beyond the utility of this protocol, the strategy demonstrated here should inspire the development of methods providing complete sets of stereoisomers for other valuable synthetic targets.

Cyclopent-2-enylaluminium as allylzinc precursor for the diastereoselective allylmetallation of non-racemic imines: applications to the synthesis of enantiomerically enriched heterocycles

The generation of cyclopent-2-enylzinc from cyclopentadiene based on a titanium-catalyzed hydroalumination/transmetallation sequence is described. Applied to the allylmetallation of phenylglycinol-derived imines, this sequence leads to homoallylic amines with moderate to good stereoselectivities. The synthesis of disubstituted azetidines and piperidines illustrates the potential of the method.

Organocatalytic and enantioselective Michael reaction between α-nitroesters and nitroalkenes. Syn/anti-selectivity control using catalysts with the same absolute backbone chirality

The asymmetric and catalytic Michael reaction between α-nitroesters and nitroalkenes has been studied in the presence of two bifunctional catalysts both containing the same absolute chirality at the carbon backbone. The reaction performed in similar conditions allows us to control the syn or anti selectivity of the Michael adduct obtaining good yields and high enantiocontrol in all cases.

Stereoselective allylboration of imines and indoles under mild conditions. An in situ E/Z isomerization of imines by allylboroxines

Direct allylboration of various acyclic and cyclic aldimine, ketimine and indole substrates was performed using allylboronic acids.

Diametric stereocontrol in dynamic catalytic reduction of racemic acyl phosphonates: divergence from α-keto ester congeners

An unexpected dichotomy was observed in the Ru-catalyzed asymmetric transfer hydrogenation of acyl phosphonates: reduction proceeded from the opposite face relative to that observed in the analogous reduction of α-keto esters. The first highly selective catalytic hydrogenation of acyl phosphonates was utilized in the dynamic kinetic resolution of α-aryl acyl phosphonates, providing β-stereogenic α-hydroxy phosphonic acid derivatives.

Divergent synthesis of functionalized carbocycles through organosilane-directed asymmetric alkyne-alkene reductive coupling and annulation sequence

An organosilane-directed alkyne-alkene reductive coupling of readily available propargylsilanes is used to access densely functionalized chiral allylsilanes. The divergent reactivity of the allylsilanes can be controlled to afford a range of novel carbocyclic ring systems through an intramolecular allylation, [3+2] annulation, and Sakurai-like homodimerization.

Selective access to both diastereoisomers in an enantioselective intramolecular Michael reaction by using a single chiral organocatalyst and application in the formal total synthesis of (-)-epibatidine

Two in one: Both diastereoisomers of 4-nitro-3-substituted cyclohexanones are accessed selectively by an intramolecular Michael reaction using a single chiral aminocatalyst (see scheme). Mechanistic studies show that the reaction is selective for the cis-diastereoisomer and that the trans-diastereoisomer arises over time. DFT calculations suggest that the cis-selectivity is due to a favorable electrostatic interaction between the iminium ion and the nucleophile.

Stereoselective cross-coupling between allylic alcohols and aldimines

A cross-coupling reaction between an allylic alcohol and an imine is described for stereoselective allylation of aromatic and aliphatic imines. This method provides operationally simple, enantioselective access to functionalized homoallylic amines. Particularly noteworthy is direct use of a functionalized allylic alcohol as an allylating reagent without prederivatization, which obviates the use of preformed organometallic reagents or activated imine derivatives.