The Phosphinoboration Reaction

Abstract

The synthesis of phosphinoboronate esters containing a single P-B bond is reported, together with preliminary reactivity studies towards a range of organic substrates. These compounds add readily to aldehydes, ketones, aldimines, and α,β-unsaturated enones to give primarily the corresponding 1,2-addition products containing a new P-C bond. The first examples of transition-metal-catalyzed phosphinoborations of C-C multiple bonds in which P-C and B-C bonds are formed in a single step are also disclosed; allenes react by a highly regioselective 1,2-addition whereas terminal alkynes undergo a formal 1,1-addition.

Double Phosphinoboration of CO2: A Facile Route to Diphospha‐Ureas

“…The first example of ad iphospha-urea (R = Ph) was preparedi nlow yieldb yt he reaction of Ph 2 PSiMe 3 with phosgene at À110 8C. [21] Subsequently,W estcott and co-workersr eported relateda ddition reactions in which Ph 2 PBpin reacts with unsaturatedm ultiple bonds prompting phosphinoboration of ketones, imines, aldehydes, [22] N-heterocycles, [23] and as eries of heteroallenes. [18] Although transition-metalsupported diphospha-ureas have also been reported, [19] we have recentlyd escribed as ynthetic route exploiting nucleophilic attack of the phosphaketene Ph 3 GePCO by phosphides and subsequenta lkylation.…”

Ruthenium-Catalyzed Regioselective 1,4-Hydroboration of Pyridines

“…5,6 Strategies toward the selective synthesis of dihydropyridines from pyridines are more limited. 7 While the direct catalytic hydrogenation resulted in over-reduction of pyridines to piperidines, 8 hydrosilylation, 9 silaboration, 10 phosphinoboration, 11 and hydroboration allow their selective synthesis.…”

The Phosphinoboration of N‐Heterocycles

“…Since this study we have developed an alternative synthesis for 1 based on the reaction between Ph 2 PSiMe 3 and ClBpin which gives a near quantitative yield of the desired product after only 15 mins at room temperature; this method is practical, straightforward and will lend itself to diversifying this class of compound. In addition to reacting with aldehydes, ketones, aldimines and enones, compound 1 also adds readily to pyridine at room temperature, without the aid of a catalyst or additional base, in either toluene or chloroform with selective and exclusive 1,4‐addition to afford compound 2 (Scheme ) . Monitoring the reaction by multinuclear NMR spectroscopy failed to show either the initial adduct or any of the 1,2‐addition product.…”

“…We recently initiated a program to develop novel borylation chemistry and have disclosed the results of our initial studies on the synthesis and reactivity of the phosphinoboronate ester Ph 2 PBpin ( 1 ) . The oxygen atoms of the pinacol group reduce the Lewis‐acidity of the boron atom which limits the amount of π‐donation from the phosphorus atom in 1 ; suggesting that it should be possible to control and tune the reactivity of phosphinoboronate esters in a rational manner by modifying the extent of π‐donation to boron.…”