Zwitterionic Phosphirenium Borates Derived from Bis(alkynyl)mesityl Phosphanes and Tris(pentafluorophenyl)borane

Abstract

From a series of bis(alkynyl)mesityl phosphanes 5, we prepared phosphirenium borate compounds 6 in high yields by reaction with B(C6F5)3 at room temperature. The zwitterionic compounds 6 are conveniently accessible and can be obtained with unique substitution patterns by this route. For two examples, we show the conversion of 6 to the respective 3‐borylated phosphole derivatives 7 through multiple 1,1‐carboboration reactions. In a useful one‐pot methodology, the phosphirenium borates 6 are converted to air‐stable 3‐arylated phospholes 8 by a sequential 1,1‐carboboration/ Suzuki–Miyaura type cross‐coupling reaction.

Heavier element-containing aromatics of [4n+2]-electron systems

“…Thermolysis of the phosphirenium borates resulted in the formation of the 1,1-carboboration products 6-8-2 or phospholes 6-8-3. [298][299][300][301][302][303][304][305] In 2016, Erker and co-workers demonstrated the reaction of allene 6-9-1 with Piers' borane, HB(C6F5)2 to give zwitterionic phosphonium borate a3CP13 (Scheme 6-9). 306 Heating of a3CP13 for 6 days in toluene at 110 °C underwent internal nucleophilic aromatic substitution to form 6-9-2.…”

FLPNO Nitroxide Radical Formation by a 1,1-Carboboration Route

“…The reaction of 7a and 7b took a different course than the one with 7c . Both alkynyl groups in the systems 7 bear substituents at their ends that have previously been shown to serve as good migrating groups in 1,1-carbo­boration reactions. , In the systems 7a and 7b , the PAr 2 substituents became the favored migrating groups under our typical reaction conditions. We isolated the products 8a and 8b formed by selective 1,1-carbo­boration at the respective CC-PAr 2 moiety in good yields.…”

Advanced 1,1-carboboration reactions with pentafluorophenylboranes

“…At slightly elevated temperatures the corresponding boryl substituted phospholes 49 were obtained in good yields (see Scheme 13 ). 38 The reaction course was followed by temperature dependent 31 P NMR spectroscopy. In this way we were able to observe some intermediates of the typical sequential 1,1-carboboration pathway along the way ranging from initial phosphane/borane adduct formation through the stages of the phosphirenium/borate zwitterion formation followed by the 1,1-carboboration product isomers at the first alkynyl unit, all the way to the final phosphole products.…”