title: Enhancing the reactivity of 1,2-diphospholes in cycloaddition reactions.
abstract: Two different approaches have been employed to enhance the reactivity of 1-alkyl-1,2-diphospholes - the introduction of electron-withdrawing groups either at the phosphorus atoms or in the para-position of the arene ring. The alkylation of sodium 1,2-diphospha-3,4,5-triphenylcyclopentadienide with alkyl halides Hal-CH2-R (R = CN, COOEt, OMe, CH2OEt) results in corresponding 1-alkyl-3,4,5-triphenyl-1,2-diphospholes (alkyl = CH2CN (1a), CH2COOEt (1b), CH2OMe (1c), and (CH2)2OEt (1d)), which spontaneously undergo the intermolecular [4 + 2] cycloaddition reactions at room temperature to form the mixture of the cycloadducts, 2a-c, respectively. However the alkylation of sodium 1,2-diphospha-3,4,5-tri(p-fluorophenyl)cyclopentadienide with ethyl iodide leads to stable 1-ethyl-3,4,5-tris(p-fluorophenyl)-1,2-diphosphole (1e), which forms the [4 + 2] cycloadduct 2,3,4,4a,5,6-hexa(p-fluorophenyl)-1-ethyl-1,7,7a-triphospha-4,7-(ethylphosphinidene)indene (2e) only upon heating up to 60 °C. With further heating to 120 °C with N-phenylmaleimide, the cycloadducts 2a-c and 2e undergo the retro-Diels-Alder reaction and form only one product of the [4 + 2] cycloaddition reaction 3a-с, 3e with good yields up to 65%.
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Almaz
authors: A
authors: Zagidullin
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Vasili
authors: V
authors: Miluykov
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Elena
authors: E
authors: Oshchepkova
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Artem
authors: A
authors: Tufatullin
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Olga
authors: O
authors: Kataeva
authors: A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre, Russian Academy of Sciences, Arbuzov Str. 8, 420088 Kazan, Russia.
authors: Oleg
authors: O
authors: Sinyashin
keywords: cycloaddition; phospholes; phosphorus heterocycles; polycyclic phosphines; retro-Diels–Alder reaction