One-pot transformation of cyclic phosphine oxides to phosphine–boranes by dimethyl sulfide–borane

Abstract

Different types of cyclic phosphine oxides, such as tetrahydrophosphole oxide 1, phosphabicyclo[3.1.0]hexane 3oxide 8 and phosphabicyclo[2.2.1]heptene 7-oxides 10 and 12 were efficiently converted to phosphine-boranes 2, 9, 11 and 13, respectively, under relatively mild conditions by reaction with 4.4 equivalents of dimethyl sulfide-borane. The more strained hetero-ring the starting phosphine oxide (in general 16) has, the easier to accomplish the change in the P-function, that takes place through the corresponding phosphine intermediate ( 20). It is noteworthy that the imide carbonyl groups in starting materials 10 and 12 were fully reduced by the borane to give 11 and 13 respectively.

Recycling the Waste: The Development of a Catalytic Wittig Reaction

“…This supports the suggestion that 1 is easier to reduce than triphenylphosphine oxide owing to the relief of ring strain, optimization of which may lead to more efficient catalyst recycling. [25] Following protocol optimization, a substrate evaluation was undertaken (Scheme 3). Notable results were that heterocyclic aldehydes could be employed, with 5 and 7 produced in high yield with diastereocontrol (E/Z); also the synthesis of 10 and 19 from citronellal, and stilbenes 17 and 18 from the corresponding benzyl bromides proceeded in high yields.…”

“…[24] In order to ensure a reasonable rate of phosphine oxide reduction, we decided to employ 3-methyl-1-phenylphospholane-1-oxide (1, Scheme 2) rather than triphenylphosphine oxide, as the former is more easily reduced. [25] After experimentation we discovered that 1 could be reduced at a reasonable rate (reduction in < 30 min) to phosphine by diphenylsilane in toluene at 100 8C. Following optimization of reduction conditions we proceeded to construct the catalytic cycle.…”

A new family of platinum(II) complexes incorporating five‐ and six‐membered cyclic phosphine ligands

“…The chosen P-heterocycles, 3-methyl-and 3,4-dimethyl-1-phenyl-3-phospholene oxides (1a [26] and 1b [27], respectively), 3-methyl-and 3,4-dimethyl-1-phenylphospholane oxides (5a [28] and 5b [29], respectively), 4-dichloromethylene-3,5-dimethyl-1-phenyl-1,4-dihydrophosphinine oxide 9 [30], and 5-methyl-1-phenyl-4-chloro-1,2,3,6-tetrahydrophosphinine oxide 12 [31] were subjected to a standard deoxygenation procedure by trichlorosilane in the presence of pyridine in boiling toluene [32]. With one exception (10), the phosphines so obtained, 2a, 2b, 6a, 6b, and 13 were reacted with dimethylsulfide borane and identified as the corresponding phosphine-boranes 3a, 3b, 7a, 7b, and 14, respectively.…”

“…Phospholane oxides 5a and 5b were synthesized by the catalytic hydrogenation of compounds 1a and 1b [28,29].…”

The Phosphine‐Catalyzed Wittig Reaction: A New Vista for Olefin Synthesis?

“…However, in late 2009 the O'Brien group from The University of Texas at Arlington reported the discovery of a viable combination of an appropriate in situ generated phosphine "1-cat" [12] and reducing agent. A screen of silanes ("P=O" reducing agent), solvents, and temperature in combination with the phosphine oxide precatalyst (1), promoted a catalytic Wittig reaction of methyl bromoacetate and benzaldehyde (Scheme 3).…”