Primary allylic amines serve as suitable allylic electrophiles for the allylation reactions of hypophosphorous acid and H-phosphinic acids. In the presence of tris(dibenzylideneacetone)dipalladium(0) ([Pd₂(dba)₃], 0.1 mol %) and Xantphos (0.2 mol %), aqueous hypophosphorous acid was allylated by α-unbranched primary allylic amines in a highly regioselective fashion to give structurally diverse allylic H-phosphinic acids in good to excellent yields with exclusive E selectivity. Moreover, increasing the catalyst loading to 1 mol % and adding aqueous phosphoric acid (1.2 equiv.) permitted the allylation of H-phosphinic acids with α-unbranched primary allylic amines to proceed to give disubstituted phosphinic acids in good to excellent yields.

An unprecedented deammoniative condensation reaction of primary allylic amines with nonallylic amines has been developed through CN bond cleavage. In the presence of 5 mol% palladium diacetate, 10 mol% 1,4-bis(diphenylphosphino)butane (dppb), and 5 mol% p-toluenesulfonic acid (TsOH), a range of α-unbranched primary allylic amines smoothly underwent deammoniative condensation with nonallylic amines in an α-selective fashion to give structurally diverse secondary and tertiary amines in good to excellent yields and E selectivity. Replacing dppb with racemic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) permitted the deammoniative condensation of enantioenriched α-chiral primary allylic amines with nonallylic amines to proceed with complete retention of configuration. Electrospray ionization (ESI) mass spectrometric analysis of the reaction mixture permitted the identification of some π-allylpalladium intermediates, and plausible mechanisms have been proposed to account for the regioselectivity and stereospecificity of the deammoniative condensation reaction.

A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid-catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities.

A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid-catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities.

An unprecedented oxidative arylation reaction of terminal alkenes with simple aroyl hydrazides has been developed under aerobic conditions for the stereoselective synthesis of 1,2-disubstituted alkenes. A range of aroyl hydrazides underwent palladium/copper-catalyzed oxidative Mizoroki–Heck reaction with terminal alkenes open to air in a 1:1 mixture of dimethyl sulfoxide and acetonitrile to give structurally diverse 1,2-disubstituted alkenes in moderate to excellent yields with excellent regio- and E-selectivity. The reaction tolerated a wide variety of functional groups, such as alkoxy, hydroxy, amino, fluoro, chloro, bromo, cyano, nitro, ester, amide, imide, phosphine oxide, and sulfone groups, and, moreover, molecular oxygen and dimethyl sulfoxide were demonstrated to serve as terminal oxidants. This study provides a useful method for the stereoselective synthesis of 1,2-disubstituted alkenes through direct transformation of the vinylic CH bonds in terminal alkenes.

A highly regioselective halogenation reaction of symmetrical and unsymmetrical aromatic azo compounds has been developed at room temperature or at 50 °C. In the presence of 5 mol% palladium diacetate and 0.5 equiv. of p-toluenesulfonic acid, a range of symmetrical aromatic azo compounds smoothly undergo monobromination with N-bromosuccinimide to give the corresponding unsymmetrical aromatic azo compounds in good to excellent yields with >99:1 ortho-selectivity. This chemistry has been successfully extended to unsymmetrical aromatic azo compounds, whose electron-richer aryl groups prefer to be monobrominated. Moreover, replacing N-bromosuccinimide with N-iodosuccinimide in the reaction allows the synthesis of monoiodinated aromatic azo compounds with >99:1 regioselectivity.

A range of polysubstituted indolenines (3H-indoles) smoothly underwent an L-proline-catalyzed enantioselective Mannich reaction with various ketones in a highly regioselective manner to give structurally diverse 2-acylmethylindolines in good yields with excellent ee. The current study provides a powerful approach for the transformation of unactivated five-membered cyclic aldimines into optically active nitrogen-containing heterocycles with high enantioselectivity.

An unprecedented olefination reaction of secondary amines with carbon nucleophiles has been developed through C–N/C–H functionalization under metal-free oxidative conditions. In the presence of a stoichiometric amount of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), a range of secondary N-alkylanilines smoothly underwent oxidative olefination with 2-alkylazaarenes, acetophenone, and malononitrile to give structurally diverse polysubstituted alkenes in moderate to excellent yields with excellent (E) selectivity. Preliminary mechanistic studies revealed that the oxidative olefination reaction proceeds through amine oxidation followed by imine olefination.

An unprecedented decarboxylative alkylation reaction of β-keto acids with isochromans has been developed under oxidative conditions. A range of β-keto acids smoothly undergo decarboxylative alkylation with isochromans in the presence of 2,2,6,6-tetramethylpiperdine-1-oxoammonium hexafluorophosphate to give structurally diverse 1-acylmethylisochromans in moderate to excellent yields with extremely high regioselectivity.

An unprecedented catalytic asymmetric synthesis of aminal-containing heterocyclic compounds has been developed from imines and tethered nitrogen/nitrogen nucleophiles. In the presence of 10 mol% of a commercially available chiral phosphoric acid, a range of aromatic, α,β-unsaturated, and aliphatic imines react with 2-aminobenzamides to give dihydroquinazolinones in good to excellent yields and ee. The enantioselectivity is significantly affected by the imine N-substituent through non-bonding interactions with the chiral phosphoric acid and the 2-aminobenzamide.

The rearrangement/oxidation of N,N-disubstituted anilines and the formal dehydrogenative cross-coupling of diarylmethanols with aniline derivatives have been developed for the preparation of symmetric and unsymmetric functionalized triarylmethanols. Both reactions proceed smoothly in trifluoroacetic acid in the presence of an inexpensive oxidant (manganese dioxide or potassium persulfate) and a catalytic amount of palladium diacetate to give a range of functionalized triarylmethanols in moderate to good yields and with extremely high regioselectivity. The two unprecedented reactions involve tandem formation of geminal CC and CO bonds, and they are synthetically useful, atom-efficient, and operationally simple.

An efficient cross-coupling reaction of N-allylic sulfonimides with organozinc reagents has been developed. In the presence of 1 mol-% of Pd₂(dba)₃, a range of N-allylic sulfonimides smoothly couple with various organozinc reagents at room temperature to give the corresponding (E)-alkene products in moderate to excellent yields and with good to exclusive α-selectivity. It is noteworthy that allyl ether, benzyl ether, and ester are tolerated under the reaction conditions.

Depending on their structures, imines are able to undergo either olefination or vicinal difunctionalization with various α-(benzothiazol-2-ylsulfonyl) carbonyl compounds in the absence of external bases. The olefination reaction of aromatic imines with α-(benzothiazol-2-ylsulfonyl) carbonyl compounds proceeds smoothly in tetrahydrofuran at 70 °C to give structurally diverse α,β-unsaturated esters, amides, and ketones in good to excellent yields and with extremely high (E) selectivity. In contrast, the carbon–nitrogen double bonds of cyclic imines and the carbon–carbon double bonds of α,β-unsaturated imines are subjected to regiospecific vicinal difunctionalization with α-(benzothiazol-2-ylsulfonyl) carbonyl compounds under the same reaction conditions to give a variety of benzothiazole derivatives in good to excellent yields. It is noteworthy that the benzothiazole moiety is present in a number of antitumor agents and bioluminescent molecules. In addition, plausible reaction pathways have been proposed to account for these transformations, and these are substantially supported by ESI-MS analysis of the reaction mixtures.

Sulfonyl-activated sp³ carbon-nitrogen bonds have been found to be cleaved by Grignard reagents in the presence of 5 mol% of copper(I) iodide (CuI). Significantly, a broad range of sulfonyl-activated benzylic, allylic, and propargylic amines smoothly undergo the cross-coupling reaction with Grignard reagents to afford structurally diverse coupling products in good to excellent yields and with high chemo-, regio-, and stereoselectivity. Moreover, an S_N2 mechanism has been demonstrated to be involved in the cross-coupling reaction that allows the asymmetric synthesis of chiral hydrocarbons from optically active α-branched amine derivatives.

An unprecedented protocol has been developed for thestereoselective synthesis of structurally diverse electron-deficient alkenes in moderate to excellent yields from readily accessible N-sulfonyl imines and stabilized phosphonium ylides. Significantly, the olefination reaction of N-sulfonylimines with nitrile-stabilized phosphonium ylides affords an array of α,β-unsaturated nitriles with high Z selectivity, and the reactions with ester-, amide-, and ketone-stabilized phosphonium ylides afford α,β-unsaturated esters, amides, and ketones with high E selectivity, respectively. Spectroscopic analysis of the reaction mixtures and trapping of the intermediates allow plausible mechanisms to be proposed. Initialimine/ylide addition leads to the formation of betaines that cyclize to form 1,2-azaphosphetanes that subsequently eliminate iminophosphoranes to yield alkenes. For the synthesis of electron-deficient 1,2-disubstituted alkenes, the presence of an electron-withdrawing group in the betaine allows rapid interconversion between its two diastereomers through proton transfer. The Z/E selectivity for alkene synthesis is determined by the different rates at which the two betaine diastereomers form the corresponding 1,2-azaphosphetane diastereomers. In contrast, the Z/E selectivity for the synthesis of electron-deficient trisubstituted alkenes originates from the diastereoselective addition of stabilized phosphonium ylides to N-sulfonyl imines.

Multicomponent reactions are a very powerful tool for the construction of complex organic molecules by using readily available starting materials. While most of the multicomponent reactions discovered so far consist of three components, the reactions with four or more components remain sparse. We have successfully developed several four-component reactions using a catalytic amount of water as a hydrolyzing agent to decompose byproduct chlorotrimethylsilane (TMSCl) to yield secondary byproduct HCl that serves as a catalyst. In the presence of 40 mol % of water, the four-component reaction of aldehydes with hexamethyldisilazane (HMDS), chloroformates, and silylated nucleophiles proceeds smoothly at room temperature to give a range of protected primary amines in moderate to excellent yields. Importantly, a wide variety of protic carbon nucleophiles, such as β-keto esters, β-diketones, and ketones, have further been explored as suitable substrates for the synthesis of protected β-amino esters and β-amino ketones that are useful building blocks for various pharmaceuticals and natural products. These four-component reactions proceed through a pathway of tandem nitrogen protection/imine formation/imine addition, and the decomposition of byproduct TMSCl, generated in the first step of nitrogen protection, with water results in the formation of secondary byproduct HCl, a strong Brønsted acid that catalyzes the following imine formation/imine addition. Taking advantage of the fact that alcohols or phenols are also able to decompose byproduct TMSCl to yield secondary byproduct HCl, no catalyst is needed at all for the four-component reactions with aldehydes bearing hydroxy groups.

The acid-catalyzed benzylic and allylic alkylation of protic nucleophiles is fundamentally important for the formation of carboncarbon and carbonheteroatom bonds, and it is a formidable challenge for benzylic and allylic amine derivatives to be used as the alkylating agents. Herein we report a highly efficient benzylic and allylic alkylation of protic carbon and sulfur nucleophiles with sulfonamides through double Lewis acid catalyzed cleavage of sp³ carbon–nitrogen bonds at room temperature. In the presence of a catalytic amount of inexpensive ZnCl₂-TMSCl (TMSCl: chlorotrimethylsilane), 1,3-diketones, β-keto esters, β-keto amides, malononitrile, aromatic compounds, thiols, and thioacetic acid can couple with a broad range of tosyl-activated benzylic and allylic amines to give diversely functionalized products in good to excellent yields and with high regioselectivity. Furthermore, the cross-coupling reaction of 1,3-dicarbonyl compounds with benzylic propargylic amine derivatives has been successfully applied to the one-step synthesis of polysubstituted furans and benzofurans.

The direct employment of benzylic and allylic alcohols as N-alkylating agents provides a useful synthetic route for amine derivatives by avoiding the preactivation of the hydroxy groups of alcohols. Herein we report a novel by-product-catalyzed three-component synthesis of amine derivatives from readily available benzylic and allylic alcohols, acyl chlorides (chloroformates or sulfonyl chlorides), and hexamethyldisilazane (HMDS). In the absence of external catalysts and additives, a range of benzylic and allylic alcohols have been transformed into the corresponding N-alkyl amides (carbamates or sulfonamides) in good to excellent yields. Furthermore, by-product TMSCl and its decomposition into HCl have been found to be responsible for promoting the three-component reaction of benzylic (or allylic) alcohols with acyl chlorides (chloroformates or sulfonyl chlorides) and HMDS.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)