Generation and stereoselective transformations of 3-phenylcyclopropene

Synthesis of 1-(2,2-Dimethylpropyl)-Cyclopropene (1-DCP) as an Ethylene Antagonist

Ethylene is a gaseous hydrocarbon molecule known as a plant hormone that promotes fruit ripening and senescence. Efficiently controlling ethylene is a central key to maintaining the quality of agricultural products. The current study uncovered a synthetic method for 1-(2,2-dimethylpropyl)-cyclopropene (1-DCP) as a cyclopropene derivative to inhibit ethylene action in fruit ripening and senescence. We synthesized 1-DCP using α-diisobutylene through a two-step process, including allylic chlorination by hypochlorite and HCl, followed by α-elimination of the allylic chloride using a strong base, lithium diethylamide. GC-MS and NMR analyses demonstrated that 1-DCP was synthesized efficiently with 35% yield and 95% purity. When treated as an aqueous emulsion on plants, including persimmon and banana fruits, 1 mM 1-DCP showed effective inhibition of ethylene action by delaying the flesh softening and peel degreening, which are representative phenomena of fruit ripening and senescence induced by ethylene. Our data demonstrated that 1-DCP could be synthesized and used as a sprayable ethylene antagonist for pre- or post-harvest growth regulation in plants and fruits.

Modular, Concise, and Efficient Synthesis of Highly Functionalized 5-Fluoropyridazines by a [2 + 1]/[3 + 2]-Cycloaddition Sequence

An easy access to 5-fluoropyridazines by a [2 + 1]/[3 + 2]-cycloaddition sequence between terminal alkynes, a difluorocarbene, and a diazo compound is reported. This approach does not necessitate the isolation of any intermediates, and a wide range of novel 5-fluoropyridazines was synthesized from readily available starting materials. Additionally, these compounds were used as a platform to access novel and highly diversified pyridazines.

Metalloradical approach to 2H-chromenes

Cobalt(III)-carbene radicals, generated through metalloradical activation of salicyl N-tosylhydrazones by cobalt(II) complexes of porphyrins, readily undergo radical addition to terminal alkynes to produce salicyl-vinyl radical intermediates. Subsequent hydrogen atom transfer (HAT) from the hydroxy group of the salicyl moiety to the vinyl radical leads to the formation of 2H-chromenes. The Co(II)-catalyzed process can tolerate various substitution patterns and produces the corresponding 2H-chromene products in good isolated yields. EPR spectroscopy and radical-trapping experiments with TEMPO are in agreement with the proposed radical mechanism. DFT calculations reveal the formation of the salicyl-vinyl radical intermediate by a metalloradical-mediated process. Unexpectedly, subsequent HAT from the hydroxy moiety to the vinyl radical leads to formation of an o-quinone methide intermediate, which dissociates spontaneously from the cobalt center and easily undergoes an endocyclic, sigmatropic ring-closing reaction to form the final 2H-chromene product.

Kinetic resolution in asymmetric epoxidation using iminium salt catalysis

The first reported examples of kinetic resolution in epoxidation reactions using iminium salt catalysis are described, providing up to 99% ee in the epoxidation of racemic cis-chromenes.