Alkyl Cyclopropyl Ketones in Catalytic Formal [3 + 2] Cycloadditions: The Role of SmI Catalyst Stabilization.

Alkyl cyclopropyl ketones are introduced as versatile substrates for catalytic formal [3 + 2] cycloadditions with alkenes and alkynes and previously unexplored enyne partners, efficiently delivering complex, sp-rich products. The key to effectively engaging this relatively unreactive new substrate class is the use of SmI as a catalyst in combination with substoichiometric amounts of Sm; the latter likely acting to prevent catalyst deactivation by returning Sm to the catalytic cycle. In the absence of Sm, background degradation of the SmI catalyst can outrun product formation.

A catalytic alkene insertion approach to bicyclo[2.1.1]hexane bioisosteres.

C(sp)-rich bicyclic hydrocarbon scaffolds, as exemplified by bicyclo[1.1.1]pentanes, play an increasingly high-profile role as saturated bioisosteres of benzenoids in medicinal chemistry and crop science.

Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones.

Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their "hard" or "soft" character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones.

Visible-Light Controlled Divergent Catalysis Using a Bench-Stable Cobalt(I) Hydride Complex.

While the use of visible light in conjunction with transition metal catalysis offers powerful opportunities to switch between on/-off states of catalytic activity, the next frontier would be the ability to switch the actual function of the catalyst and resulting products. Here we report such an example of multi-dimensional catalysis. Featuring an easily prepared, bench-stable cobalt(I) hydride complex in conjunction with pinacolborane, we can switch the reaction outcome between two widely employed transformations, olefin migration and hydroboration, with visible light as the trigger.

Characterization of Jasmonoyl-Isoleucine (JA-Ile) Hormonal Catabolic Pathways in Rice upon Wounding and Salt Stress.

Background: Jasmonate (JA) signaling and functions have been established in rice development and response to a range of biotic or abiotic stress conditions. However, information on the molecular actors and mechanisms underlying turnover of the bioactive jasmonoyl-isoleucine (JA-Ile) is very limited in this plant species.

Results: Here we explored two gene families in rice in which some members were described previously in Arabidopsis to encode enzymes metabolizing JA-Ile hormone, namely cytochrome P450 of the CYP94 subfamily (CYP94, 20 members) and amidohydrolases (AH, 9 members).

Tertiary Enamide-Triggered SAr: Domino Allylation and Enamine-Type Addition.

Two unprecedented domino reactions are described, starting from ketospiro-enesulfonamides. By treatment with ZrCl and allylsilane, an intramolecular electrophilic aromatic substitution and subsequent allylation is observed. By treatment with TiCl and allylsilane, a double enamine-type reaction takes place, thus creating simultaneously four contiguous stereogenic centers diastereoselectively.

A 2',2'-disulfide-bridged dinucleotide conformationally locks RNA hairpins.

The synthesis and the impact of a disulfide bridge between 2'-O-positions of two adjacent nucleotides in an RNA duplex and in the loop of RNA hairpins are reported. The incorporation of this 2',2'-disulfide (S-S) bridge enabled thermal and enzymatic stabilization of the hairpin depending on its position in the loop. The influence of the disulfide bridge on RNA folding was studied at the HIV Dimerization Initiation Site (DIS) as an RNA sequence model.

Direct Spirocyclization from Keto-sulfonamides: An Approach to Azaspiro Compounds.

Spontaneous spirocyclization of keto-sulfonamides via ynamides through a one-pot process is presented. Push-pull ynamides were obtained through Michael addition/elimination without Cu. The obtained azaspiro compounds are building blocks for indole alkaloids.