Steroe- and chemoselectivity in 1,3-dipolar cycloaddition reaction of 2-diazopropane with diarylidenacetones

Synthesis and Photolysis of Hexahydropyrrolo[3,4-c]pyrazole derivatives

The 1,3-dipolar cycloaddition of 2-diazopropane 1 with N-arylcitraconimides and N-arylmaleimides 2, at −78°C, has led to monoadducts 3. The same addition of 2-diazopropane with maleimide 4, has led to a new and unexpected Δ3-1,3,4-oxadiazoline 5. Irradiation of the pyrazolines 3 led to clean extruction of nitrogen to give the cyclopropanes 6.

Reaction of C-Silylated α-Diazophosphines as Nucleophiles toward Carbonyl Compounds: A Mechanistic Study and Application to the Synthesis of Alkynes and α-Hydroxyphosphonamides

Diversely substituted alpha-hydroxyphosphonamides and alkynes have been efficiently synthesized through the reaction of C-silylated alpha-diazophosphines with different types of aldehydes (2 equiv) in a neutral medium under very mild conditions. The reaction with some chiral aldehydes is highly diastereoselective leading to phosphonamides as single diastereomers. The novel reaction is influenced by electronic and steric effects being precluded for aromatic aldehydes containing electron-releasing substituents on the phenyl ring and for bulky aliphatic aldehydes. The mechanistic studies of these processes, which are highly exothermic, provide evidence for a nucleophilic attack of the diazophosphine to the aldehyde leading to a betaine that rapidly rearranges to a diazomethylenephosphorane, which has been detected or captured in some instances. The diazomethylenephosphorane reacts with a second molecule of aldehyde according to a Wittig-type condensation, and the rate-determining step of the whole process is believed to be the decomposition of the resultant oxaphosphetane to afford the hydroxyphosphonamide and a diazocumulene. Finally, this intermediate loses molecular nitrogen giving a transient carbene that rapidly evolves toward the alkyne.

Synthesis and Structural Elucidation of Novel Spiropyrazolines Precursors to Spiro-gem-dimethylcyclopropanes

1,3-dipolar cycloaddition reaction of 2-diazopropane (DAP) 1 with 2-arylidene-1-tetralone 2a–b led exclusively to spiro-Δ1-pyrazolines 3a–b. When 4-methyl-2-arylidene-1-tetralones 2c–d was used as starting dipolarophile a mixture of diastereiosomeric cycloadducts 4a–b and 5a–b was obtained. The photochemical nitrogen-extrusion studied for spiropyrazolines 3a–b and 4a–b led stereospecifically to spiro-gem-dimethylcyclopropanes. In all cases, the reaction regiochemistry and stereochemistry was discussed on the basis of 2D-NMR experiments.