Aqueous Synthesis of (R*,R*)-Bis(spiropyrazolone)cyclopropanes through Iodine-Promoted Cyclization of Aldehydes and Pyrazolin-5-ones

The molecular iodine promoted cyclization of aldehydes and pyrazolin-5-ones was accomplished in water using tetrabutylammonium iodide as a phase transfer catalyst, affording a variety of substituted (R*,R*)-bis(spiropyrazolone)cyclopropanes in good to excellent yields (76-96%).This aqueous reaction exhibits very high chemoselectivity, and the products were obtained by simple Büchner filtration without chromatographic isolation procedure.Cyclopropane moiety plays a prominent role in synthetic chemistry because the strained structure and unique bonding characteristics of the three-membered ring determine a variety of organic transformations. 1 Among different types of cyclopropane fragments, spirocyclopropyl moiety has been attracting much attention due to its biological activities and pharmacological properties. 2 Especially, a spirocyclopropyl moiety jointed with a heterocyclic counterpart has attracted particular attention due to its synthetic utility and wide range of pronounced pharmacological applications. 3For example, some fused spirocyclopropyl heterocycles have been recognized as α-L-fucosidase, 4 β-lactamase and HIV-1 non-nucleoside reverse transcriptase inhibitors as well as diagnostic markers for early detection of colorectal and hepatocellular cancer. 5On the other hand, as an important class of spiro-heterocycles, spiropyrazolone motifs are also ubiquitous in significantly bioactive compounds, such as antimicrobial agent, 6 anti-inflammatory agent, 7 antitumor agent, 8 analgesic agent, 9 RalA inhibitor 10 and 4-phosphodiesterase inhibitor. 11As a special kind of spiral compounds bearing both spiro-connected cyclopropane and pyrazolone scaffolds, bis(spiropyrazolone)cyclopropanes have great potential