Crystallographic characterization of a stable 7-phosphanorbornadiene-7-oxide: 2,3-benzo-1,4,5,6,7-pentaphenyl-7-phosphabicyclo[2.2.1] hepta-2,5-diene-7-oxide

Abstract

The stable 7‐phosphanorbornadiene derivative, 2,3‐benzo‐1,4,5,6,7‐pentaphenyl‐7‐phosphabicyclo[2.2.1]hepta‐2,5‐diene‐7‐oxide (1) was synthesized in 45% yield via the Diels‐Alder reaction of pentaphenylphosphole oxide and benzyne. The reaction occurs specifically to give a single isomer, which was characterized by use of X‐ray crystallography and 31P NMR spectroscopy. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:182–186, 2000

Facile Synthesis of Dibenzo-7λ3-phosphanorbornadiene Derivatives Using Magnesium Anthracene

“…The early view that “it was quite obvious that the only reasonable way to prepare 7-phosphanorbornadienes remained the [2 + 4] cycloadditions between electrophilic acetylenic dienophiles and phospholes” has been unchallenged and not fruitful in terms of delivering valuable derivatives that bear an unprotected lone pair of electrons at phosphorus. This status quo fostered a prevailing sensibility that the lone electron pair at phosphorus and the strained CPC angle impart inherent instability to the 7-phosphanorbornadiene architecture. , Protection of the phosphorus lone pair by either metal complexation − or by utilizing the corresponding phosphine oxide , allowed the isolation of stabilized derivatives. In 2000, the first unprotected 7λ 3 -phosphanorbornadiene derivative was generated (by decomplexation of a protected 7-phosphanorbornadiene) as a species not sufficiently stable for isolation in which the cheletropic loss of the aromatic moiety was disfavored by incorporation of a highly strained metacyclophane subunit …”