Comparative genomics of the niche-specific plant pathogen Streptomyces ipomoeae reveal novel genome content and organization.

IMPORTANCE: While most plant-pathogenic Streptomyces species cause scab disease on a variety of plant hosts, Streptomyces ipomoeae is the sole causative agent of soil rot disease of sweet potato and closely related plant species. Here, genome sequencing of virulent and avirulent S. ipomoeae strains coupled with comparative genomic analyses has identified genome content and organization features unique to this streptomycete plant pathogen. The results here will enable future research into the mechanisms used by S. ipomoeae to cause disease and to persist in its niche environment.

Directing the Stereoselectivity of the Claisen Rearrangement to Form Cyclic Ketones with Full Substitution at the α-Positions.

We report an enantioselective synthesis of cyclic ketones with full substitutions at the α-positions in a highly diastereoselective manner. Our method is achieved by subjecting substrate motifs in 2-allyloxyenones to chiral organomagnesium reagents, which trigger the Claisen rearrangement upon direct 1,2-carbonyl addition. The observed diastereoselectivity of the allyl migration is proposed to originate from the intramolecular chelation of the magnesium alkoxide to the allyloxy moiety.

Transition metal-catalyzed regioselective functionalization of carbazoles and indolines with maleimides.

The directing group-assisted regioselective C-H activation of carbazoles and indolines is achieved via transition metal-catalyzed reactions. This C-H functionalization protocol provides a rapid approach to install diversely functionalized succinimide groups at the C-1 position of the carbazole moiety. In addition, this protocol demonstrates the intrinsic reactivity of indolines in providing C-2 succinimide-substituted indoles via cascade direct oxidation and C-H functionalization. This protocol also provides C-7 succinimide-substituted indolines under mild reaction conditions. The features of this reaction include a wide substrate scope and excellent regioselectivity for the installation of the succinimide moiety on biologically interesting molecules.

Palladium-Catalyzed Direct Oxidative C-H Activation/Annulation for Regioselective Construction of N-Acylindoles.

A Pd(II)-catalyzed C(sp3)-H/C(sp2)-H coupling/annulation of anilides and α-dicarbonyl compounds for the synthesis of diverse N-acyl indoles is described. The reaction is achieved by cascade C-H activation, coupling, and intramolecular cyclization. This protocol provides a variety of indoles with high functional group tolerance and excellent regioselectivity. The utility of this protocol is demonstrated by transforming the synthesized compound into diversely functionalized analogues.

Palladium-catalyzed synthesis of ß-hydroxy compounds via a strained 6,4-palladacycle from directed C-H activation of anilines and C-O insertion of epoxides.

A palladium-catalyzed C-H activation of acetylated anilines (acetanilides, 1,1-dimethyl-3-phenylurea, 1-phenylpyrrolidin-2-one, and 1-(indolin-1-yl)ethan-1-one) with epoxides using O-coordinating directing groups was accomplished. This C-H alkylation reaction proceeds via formation of a previously unknown 6,4-palladacycle intermediate and provides rapid access to regioselectively functionalized ß-hydroxy products. Notably, this catalytic system is applicable for the gram scale mono-functionalization of acetanilide in good yields. The palladium-catalyzed coupling reaction of the ortho-C(sp2) atom of O-coordinating directing groups with a C(sp3) carbon of chiral epoxides offers diverse substrate scope in good to excellent yields. In addition, further transformations of the synthesized compound led to biologically important heterocycles. Density functional theory reveals that the 6,4-palladacycle leveraged in this work is significantly more strained (>10 kcal mol-1) than the literature known 5,4 palladacycles.

Rhodium(iii)-catalyzed regioselective distal ortho C-H alkenylation of N-benzyl/furanylmethylpyrazoles directed by N-coordinating heterocycles.

C-H activation of challenging N-benzylpyrazoles was accomplished by employing rhodium(iii) catalysis. This C-H activation reaction proceeds via a six-membered rhodacycle intermediate and enables distal regioselective alkenyl-functionalization on the aromatic ring of N-benzylpyrazoles without the formation of bis-adducts. High functional group tolerance, low catalyst loading, and superior reactivity of olefin moieties towards N-benzylpyrazoles are some of the attractive features of this protocol. This protocol offers a broad scope for the regioselective functionalization of indazoles, benzo[d][1,2,3]triazoles, and 1-(furan-3-ylmethyl)-1H-pyrazole in good yields.

Ruthenium catalyzes the synthesis of γ-butenolides fused with cyclohexanones.

Ruthenium(II)-catalyzed reactions of cyclic diazodicarbonyl compounds with ß-ketoamides for chemo- and stereoselective construction of cyclohexanone-fused γ-butenolides are described. This study represents the first example of the addition of an enol substrate which is formed by the tautomerization of the ß-ketoamides to the electrophilic carbene center for unusual cyclization through amide cleavage. The combined experimental and computational studies shed light on the mechanistic pathway favouring the unusual ring formation reaction instead of the involvement of the general carbonyl ylide intermediates for the product generation.

Chitosan-derived N-doped carbon catalysts with a metallic core for the oxidative dehydrogenation of NH-NH bonds.

Sustainable metal-encased (Ni-Co/Fe/Cu)@N-doped-C catalysts were prepared from bio-waste and used for the oxidative dehydrogenation reaction. A unique combination of bimetals, in situ N doping, and porous carbon surfaces resulted in the formation of the effective "three-in-one" catalysts. These N-doped graphene-like carbon shells with bimetals were synthesized via the complexation of metal salts with chitosan and the subsequent pyrolysis at 700 °C. A well-developed thin-layer structure with large lateral dimensions could be obtained by using Ni-Fe as the precursor. Importantly, the Ni-Fe@N-doped-C catalyst was found to be superior for the dehydrogenation of hydrazobenzene under additive/oxidant-free conditions compared to the conventional and other synthesized catalysts. Characterizations by TEM and XPS accompanied by BET analysis revealed that the enhanced catalytic properties of the catalysts arose from their bimetals and could be attributed to the graphitic shell structure and graphitic N species, respectively.

Synergistic Indium and Silver Dual Catalysis: A Regioselective [2 + 2 + 1]-Oxidative N-Annulation Approach for the Diverse and Polyfunctionalized N-Arylpyrazoles.

Indium(III)/silver(I)-catalyzed [2 + 2 + 1] annulation of arylhydrazine hydrochlorides with ß-enamino esters via multicomponent reactions for the construction of diverse and multisubstituted N-arylpyrazoles has been demonstrated. The oxidative cycloaddition proceeds via a cascade triple Michael addition/elimination/air oxidation. This novel protocol provides a rapid and efficient synthetic route to various 3,4-diester-substituted N-arylpyrazoles. The synthesized compounds are further utilized for various synthetic transformations.

Total synthesis of the natural product EBC-329.

The first total synthesis of an anti-leukemic diterpene natural product EBC-329 (1) has been accomplished starting from readily available 6,6-dimethyl-3-oxabicyclo[3.1.0]hexane-2,4-dione (7). An efficient and general approach has been reported for the synthesis of EBC-329 in 13 steps with an overall yield of 10%.