Enantioselective Reductive Cyanation and Phosphonylation of Secondary Amides by Iridium and Chiral Thiourea Sequential Catalysis.

The combination of transition-metal catalysis and organocatalysis increasingly offers chemists opportunities to realize diverse unprecedented chemical transformations. By combining iridium with chiral thiourea catalysis, direct enantioselective reductive cyanation and phosphonylation of secondary amides have been accomplished for the first time for the synthesis of enantioenriched chiral α-aminonitriles and α-aminophosphonates. The protocol is highly efficient and enantioselective, providing a novel route to the synthesis of optically active α-functionalized amines from the simple, readily available feedstocks.

Chemoselective Synthesis of α-Amino-α-cyanophosphonates by Reductive Gem-Cyanation-Phosphonylation of Secondary Amides.

A novel approach to α-amino-α-cyanophosphonates has been developed. The method features a TfO-mediated reductive geminal cyanation/phosphonylation of secondary amides. Mild reaction conditions, high bond-forming efficiency, inexpensive readily available starting materials, and good to excellent yields with wide functional group compatibility constitute the main advantages of this method.

Enamines as Surrogates of Alkene Carbanions for the Reductive Alkenylation of Secondary Amides: An Approach to Allylamines.

A new strategy to construct allylamines through reductive alkenylation of secondary amides with enamines is reported. The method features the use of trifluoromethanesulfonic anhydride as an activation reagent of amides, and enamines as unconventional alkenylation reagents. In this manner, enamines serve as surrogates of alkene carbanions instead of the classical enolates equivalents.

Titanocene(III)-Catalyzed Three-Component Reaction of Secondary Amides, Aldehydes, and Electrophilic Alkenes.

An umpolung Mannich-type reaction of secondary amides, aliphatic aldehydes, and electrophilic alkenes has been disclosed. This reaction features the one-pot formation of C-N and C-C bonds by a titanocene-catalyzed radical coupling of the condensation products, from secondary amides and aldehydes, with electrophilic alkenes. N-substituted γ-amido-acid derivatives and γ-amido ketones can be efficiently prepared by the current method.

General and chemoselective bisphosphonylation of secondary and tertiary amides.

With Tf2O as the activation reagent, a mild and general method has been developed for the bisphosphonylation of both secondary and tertiary amides. The protocol is highly efficient and chemoselective, and it tolerates a number of sensitive functional groups such as cyano, ester, and aldehyde groups.

Enantioselective total synthesis of (+)-methoxystemofoline and (+)-isomethoxystemofoline.

The first enantioselective total synthesis of (+)-methoxystemofoline (2) and (+)-isomethoxystemofoline (3) has been reported. The synthesis employed the halide-assisted bromotropanonation method that we developed recently to construct the core structure, and Overman's strategy for the implementation of the butenolide moiety. Through this work, the structure of methoxystemofoline was revised as with an E-alkene, and its absolute configuration was established.

SmI2-mediated radical coupling strategy to Securinega alkaloids: total synthesis of (-)-14,15-dihydrosecurinine and formal total synthesis of (-)-securinine.

The asymmetric total synthesis of (-)-14,15-dihydrosecurinine and the formal total synthesis of (-)-securinine were accomplished starting from an easily available malimide. A concise SmI2-mediated radical coupling strategy has been developed to construct the bridged α-hydroxy 6-azabicyclo[3.2.

Direct reductive coupling of secondary amides: chemoselective formation of vicinal diamines and vicinal amino alcohols.

We report the first one-pot reductive homocoupling reaction of secondary amides and cross-coupling reaction of secondary amides with ketones to give secondary vicinal diamines and amino alcohols. This method relies on the direct generation of α-amino carbon radicals from secondary amides by activation with trifluoromethanesulfonic anhydride, partial reduction with triethylsilane and samarium diiodide-mediated single-electron transfer. The reactions were run under mild conditions and tolerated several functional groups.

A preliminary investigation of anti-reflux intervention for gastroesophageal reflux related childhood-to-adult persistent asthma.

Background: Childhood-to-adult persistent asthma is usually considered to be an atopic disease. However gastroesophageal reflux may also play an important role in this phenotype of asthma, especially when it is refractory to pulmonary medicine.

Methods: Fifty-seven consecutive GERD patients who had decades of childhood-to-adult persistent asthmatic symptoms refractory to pulmonary medication were enrolled.

Tertiary amide-based Knoevenagel-type reactions: a direct, general, and chemoselective approach to enaminones.

We report one-pot and chemoselective Knoevenagel-type reactions using highly stable amides and lactams as the electrophilic substrates. The method is based on the in situ activation of amide carbonyl with triflic anhydride and a subsequent reaction with carbanions generated in situ from carbonyl compounds. The amide-based method is an alternative to the versatile thioamide-based Eschenmoser sulfide contraction.

Complexity generation by chemical synthesis: a five-step synthesis of (-)-chaetominine from L-tryptophan and its biosynthetic implications.

We demonstrated, for the first time, that on the basis of chemistry principles, the hexacyclic peptidyl alkaloid (−)-chaetominine (1) can be synthesized in a straightforward manner from L-Trp. The approach features the efficient generation of molecular complexity via a tandem C3/C14 syn-selective epoxidation (dr = 3:2)–annulative ring-opening reaction and a regioselective epimerization at C14. The successful production of (−)-chaetominine (1) from L-Trp could be helpful for revealing how the configuration of L-tryptophan becomes inverted in the biosynthetic pathway of (−)-chaetominine (1).

Modular enantioselective synthesis of 8-aza-prostaglandin E1.

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-γ-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based α-amidalkylation protocol (dr = 6.8:1), with the chiral pre-ω-chain.

Versatile construction of functionalized tropane ring systems based on lactam activation: enantioselective synthesis of (+)-pervilleine B.

The halo-assisted intramolecular addition of silyl enol ethers with in situ activated lactams yielded (hydroxylated) 1-halo-8-azabicyclo[3,2,1]octane and 1-halo-9-azabicyclo[3,3,1]nonane ring systems, which provided an easy enantioselective access to 6β-silyloxytropane-3-one, 3α,6β-dihydroxytropane, and pervilleine B. The absolute configuration of the natural (-)-pervilleine B was determined to be 1R,3R,5S,6R.

Reductive hydroxyalkylation/alkylation of amines with lactones/esters.

We have developed a one-pot method for the direct intermolecular reductive hydroxyalkylation or alkylation of amines using lactones or esters as the hydroxyalkylating/alkylating reagents. The method is based on the in situ amidation of lactones/esters with DIBAL-H-amine complex (for primary amines) or DIBAL-H-amine hydrochloride salt complex (for secondary amines), followed by reduction of the amides with an excess of DIBAL-H. Different from the reduction of Weinreb amides with DIBAL-H where aldehydes are formed, the reduction of the in situ formed Weinreb amides yielded amines.

Enantioselective syntheses of rigidiusculamides A and B: revision of the relative stereochemistry of rigidiusculamide A.

The first enantioselective synthesis of cytotoxic natural products rigidiusculamides A (ent-21) and B (8) has been achieved by two synthetic routes. The first one is convergent based on the common intermediate 11, obtained through a high yielding SmI(2) -mediated Reformatsky-type reaction. A highly diastereoselective one-pot Dess-Martin periodinane-mediated bis-oxidation allowed the direct conversion of the diastereomeric mixture of 11 into rigidiusculamide B (8).

Concise asymmetric total synthesis of 9-epi-sessilifoliamide J.

A 10-step asymmetric synthesis of 9-epi-sessilifoliamide J (20), together with sessilifoliamide J (6), has been accomplished from the key chiral building block 11 via a threo-selective vinylogous Mannich reaction and a Ley oxidation-SmI(2)-mediated coupling lactonization. The absolute configuration of the natural sessilifoliamide J was established.

A flexible asymmetric approach to methyl 5-alkyltetramates and its application in the synthesis of cytotoxic marine natural product belamide A.

By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, methyl 5-methyltetramate (2 a) is found in cytotoxic mirabimide E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatin 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamide A (7) has been achieved in seven steps from (S)-9, with an overall yield of 23.