1lambda(3),3lambda(3)-Diphosphacyclobutadienes have been specifically generated for the first time through hexachloroethane-induced extrusion of the organophosphorus ligands from dimeric zirconocene-phosphaalkyne complexes. The species were chemically characterized indirectly by reactions with appropriate trapping reagents. Thus, the use of bis(acceptor)-substituted alkynes gave rise to 2,5-diphosphabenzvalenes, whereas reactions with N-methylmaleinimide and donor -substituted alkynes such as bis(diethylamino)acetylene resulted in the fort-nation of 1,3-diphospha-Dewar-benzenes. Representatives of both classes of compounds were analyzed by X-ray crystallography. Kinetically stabilized phosphaalkynes reacted similarly to furnish tetraphosphabishomoprismanes through a sequence of [4 + 2] and [2 + 2 + 2] cycloaddition processes. (C) 2002 Elsevier Science B.V. All rights reserved.
Homo-Diels-Alder reactions take place under very mild conditions when the 1,3,5-triphospha-Dewar-benzene derivative 4 is allowed to react with electron-deficient alkynes, such as dimethyl acetylenedicarboxylate or methyl propyonate, or with tert-butylphosphaacetylene. The resultant [2 + 2 + 2]-cycloadducts 5, 6, and 8 can be isolated in excellent yields and are formed regioselectively. Moreover, the first example of a [4 + 2 + 2]-cycloaddition has been realized by the reaction of 4 with tri-tert-butylazacyclobutadiene 10 which yields the two exo-cycloadducts 11 and 12. The cycloadduct 12 is unstable under the conditions of column chromatography on silica gel and undergoes rearrangement to the isomer 13.
Organophosphorus Compounds, 119. The Phosphaalkyne Cyclotetramer System — Syntheses, Valence Isomerizations, and Reactions
作者:Andreas Mack、Manfred Regitz
DOI:10.1002/cber.19971300703
日期:1997.7
Interestingly, these tetramers can be interconverted by various valenceisomerizations. The results of thermal and photochemically-induced rearrangements are in good agreement with MO calculations carried out for the parent compounds. Phosphaalkynecyclotetramers exhibit a highly interesting reactivity and other peculiar features. One outstanding example is the tetraphosphacubane 5, which shows unusual