Synthesis of protected α-amino acids via decarboxylation amination from malonate derivatives.

A general and efficient strategy for the synthesis of protected α-amino acids is reported. The method uses malonate derivatives as the starting materials and Cs2CO3 as a base at 60 degrees, giving α-amino acid derivatives in moderate yields by releasing CO2. This methodology shows broad substrate scope (primary and secondary acids), excellent functional group tolerance and high efficiency to give the desired products under mild reaction conditions. It also allows the construction of ß and γ-amino acids and other unnatural products.

Base-Mediated Intramolecular Decarboxylative Synthesis of Alkylamines from Alkanoyloxycarbamates.

A general and effective method for the synthesis of alkylamine via intramolecular decarboxylation of alkanoyloxycarbamates is described. The alkanoyloxycarbamates are readily prepared with alkyl carboxylic acids and hydroxylamine. The reaction shows a broad range of substrates (primary and secondary alkyl) with functional tolerance, and the corresponding products were obtained in good yields under mild conditions.

Synthesis of indoles from aroyloxycarbamates with alkynes via decarboxylation/cyclization.

An efficient Pd-catalyzed decarboxylation/cyclization of aroyloxycarbamates to realize substituted indoles has been disclosed. Terminal alkynes as the coupling partners lead to site specific 2-substituted indoles through two pathways, while internal alkynes with aroyloxycarbamates can be transformed to 2,3-disubstituted indoles directly. This protocol is further demonstrated by the efficient synthesis of indoles as well as the success of employing inexpensive aryl acids as starting materials to construct C-N bonds by releasing CO2.

Regioselective Synthesis of 2-Vinylanilines Using O-aroyloxycarba-mates by Sequential Decarboxylation/Amination/Heck Reaction.

A new sequential approach for 2-vinylanilines utilizing aryl carboxylic acids as stable, inexpensive and widely available arylating reagents is described. Employing a Pd-POVs catalyst system, this protocol is not only overcoming the restriction barrier of decarboxylative coupling to ortho-substituted substrates, but also provides site-special to create new C(sp2)-N and C(sp2)-C(sp2) bonds. Mechanistic experiments suggest the cleavage of C(sp2)-COOH gives priority to C(sp2)-X bond in this reaction.

Synthesis and Evaluation of QS-21-Based Immunoadjuvants with a Terminal-Functionalized Side Chain Incorporated in the West Wing Trisaccharide.

Three QS-21-based vaccine adjuvant candidates with a terminal-functionalized side chain incorporated in the west wing trisaccharide have been synthesized. The terminal polar functional group serves to increase the solubility of these analogues in water. Two of the synthetic analogues have been shown to have adjuvant activity comparable to that of GPI-0100. The stand-alone adjuvant activity of the new synthetic analogues again confirmed that it is a feasible way to develop new saponin-based vaccine adjuvants through derivatizing at the west wing branched trisaccharide domain. Inclusion of an additional polar functional group such as a carboxyl group (as in 3x) or a monosaccharide (as in 4x and 5x) is sufficient to increase the water solubility of the corresponding synthetic analogues to a level comparable to that of GPI-0100 and suitable for immunological studies and clinical application. The structure of the incorporated side chain has a significant impact on the adjuvant activity in terms of the magnitude and nature of the host's responses.

One-pot sequential organocatalysis: highly stereoselective synthesis of trisubstituted cyclohexanols.

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96%) synthesis of trisubstituted cyclohexanols was achieved by using a one-pot sequential organocatalysis that involved a quinidine thiourea-catalyzed tandem Henry-Michael reaction between nitromethane and 7-oxo-hept-5-en-1-als followed by a tetramethyl guanidine (TMG)-catalyzed tandem retro-Henry-Henry reaction on the reaction products of the tandem Henry-Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one-pot sequential organocatalysis by using the racemic Henry product as the substrate.

Highly stereoselective synthesis of trisubstituted cyclohexanols using a guanidine-catalyzed tandem Henry-Michael reaction.

A highly diastereoselective (dr >99:1) and enantioselective (ee value up to 98%) synthesis of trisubstituted cyclohexanols was achieved by using a tandem Henry--Michael reaction between nitromethane and 7-oxo-hept-5-enals catalyzed by the Misaki-Sugimura guanidine.

Synthesis of QS-21-based immunoadjuvants.

Three structurally defined QS-21-based immune adjuvant candidates (2a-2c) have been synthesized. Application of the two-stage activation glycosylation approach utilizing allyl glycoside building blocks improved the synthetic accessibility of the new adjuvants. The efficient synthesis and establishment of the stand-alone adjuvanticity of the examined synthetic adjuvant (2b) open the door to the pursuit of a new series of structurally defined QS-saponin-based synthetic adjuvants.

Diastereodivergent synthesis of 4-oxocyclohexanecarbaldehydes by using the modularly designed organocatalysts upon switching on their iminium catalysis.

The cinchona thiourea moiety in the self-assembled modularly designed organocatalysts (MDOs) switches off the iminium catalysis of these catalysts. In this study, it was found that the inhibited iminium catalysis could be switched on by using an appropriate weak acid and that, once the iminium catalysis was switched on, these catalysts could be applied for the highly stereoselective and diastereodivergent synthesis of 4-oxocyclohexanecarbaldehydes via a domino reaction between ketones and α,ß-unsaturated aldehydes.

Pd-Catalyzed Oxidative Heck Reaction of Grignard Reagents with Diaziridinone as Oxidant.

A novel Pd-catalyzed oxidative Heck reaction with readily available Grignard reagents using di- t-butyldiaziridinone as an oxidant has been developed. Various substituted olefins were obtained in 46-91% yields with high regioselectivity under mild reaction conditions.

Cu(i)/{Nb6O19} catalyzed N-acylation of arylacetic acids with amines under aerobic conditions.

The method described herein is a general, efficient and green approach to synthesize α-ketoamides from arylacetic acids and amines. Employing a simple copper(i)/{Nb6O19} catalyst system, the reaction offers a facile process to give functionalized α-ketoamides from readily available arylacetic acids under aerobic conditions. The merit of this new strategy is that it expands the syntheses of α-ketoamides from stable, inexpensive and widely available acylation reagents such as arylacetic acids in one step.

Palladium-Catalyzed Decarboxylative Synthesis of Arylamines.

A novel approach has been developed for the synthesis of arylamines via the palladium-catalyzed intramolecular decarboxylative coupling (IDC) of aroyloxycarbamates, obtained in situ by reacting aryl carboxylic acids with hydroxycarbamates. The reaction offers facile access to structurally diverse arylamines with the site-specific formation of the C(sp2)-N bond under mild conditions.

Highly stereoselective synthesis of 2,6-cis-substituted tetrahydropyrans using a one-pot sequential catalysis.

A catalytic highly diastereo- and enantioselective synthesis of 2,6-cis-substituted tetrahydropyrans was realized using a one-pot sequential catalysis involving Henry and oxa-Michael reactions. The nitroaldol products obtained in a highly enantioselective copper(II)-catalyzed Henry reaction between nitromethane and 7-oxo-hept-5-enals were subsequently treated with a catalytic amount of camphorsulfonic acid (CSA) to give the desired tetrahydropyran derivatives in excellent yields, diastereoselectivities (dr >99:1), and enantioselectivities (ee = 98-99%). The reaction can also be used for the high stereoselective synthesis of a cis-2,6-disubstituted morpholine.

Total syntheses of Tardioxopiperazine A, Isoechinulin A, and Variecolorin C.

First total syntheses of the isoechinulin-type alkaloids: Tardioxopiperazine A, Isoechinulin A, and Variecolorin C have been achieved from a common key intermediate 5, which was derived from a regiocontrolled Stille cross-coupling reaction of an allylindium reagent.