title: PPh3-Mediated [4 + 2]- and [4 + 1]-Annulations of Maleimides with Azoalkenes: Access to Fused Tetrahydropyridazine/Pyrrolidinedione and Spiro-dihydropyrazole/Pyrrolidinedione Derivatives.
abstract: Unprecedented PPh3-mediated [4 + 2]- and [4 + 1]-annulation of maleimides with in situ formed azoalkenes have been successfully developed, affording fused tetrahydropyridazine/pyrrolidinedione and spiro-dihydropyrazole/pyrrolidinedione derivatives in good yields under mild reaction conditions. Maleimides serve as C2 synthons in the [4 + 2]-annulation using 1,2-dichloroethane as the solvent in the presence of 20 mol % of PPh3. With a stoichiometric amount of PPh3in acetone, maleimides serve as C1 synthons, and the in situ formed phosphorus ylide is the key intermediate to realize this [4 + 1]-annulation.
authors.affiliation: College of Chemistry and Molecular Sciences, Wuhan University , Wuhan 430072, China.|State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry , Shanghai 230012, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Huang
authors.affiliation: College of Chemistry and Molecular Sciences, Wuhan University , Wuhan 430072, China.|State Key Laboratory of Elemento-organic Chemistry, Nankai University , Tianjin 300071, China.
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Tao
authors.affiliation: College of Chemistry and Molecular Sciences, Wuhan University , Wuhan 430072, China.|State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry , Shanghai 230012, China.
authors.forename: Chun-Jiang
authors.identifier: 0000-0003-3629-6889
authors.initials: CJ
authors.lastname: Wang