Potassium hydroxide, deprotonation

Interesting chemistry has been observed in the process of attaching pendant donors and propylene chloride substituents to arsenic-sulfur heterocycles <85CB2714>. The arsine oxide (84) was converted into the heterocycle (85) by reaction with 1,3-propane dithiol in the presence of potassium hydroxide. Deprotonation of this compound with LDA at — 50 °C to — 35 C afforded the 2-lithio intermediate... 

The general feature of alkylation reactions at a carbon atom is that they can be achieved under sonication using solid bases even in apolar solvents. The advantage is that side reactions are generally minimised. Deprotonation occurs readily on a benzylic position in the presence of aqueous sodium hydroxide, as shown with indene (Eq. 3.21) [117]. A quantitative yield of the alkylated product can be obtained using sonication in the presence of a PTC. It was suggested that alkylation of cyclopentadiene or indene by secondary or tertiary alkyl halides in the presence of potassium hydroxide and Ali-quat occurred via a SET process [118]. 

Carbanions can be generated and alkylated in a two-phase liquid-liquid system using concentrated aqueous sodium or potassium hydroxide as the base. Makosza has shown that deprotonation occurs at the interface, Fig. 5.10 [12]. 

Potassium hydroxide can deprotonate as weak an acid as (C6H5)3CH (pKa 32), and its desiccant properties ensure the necessary dry conditions. 

Whereas encapsulation of the small cation Ca2+ ion led to host-guest system 2 with an M/MC = 1 1 stoichiometry, double deprotonation of di-tert-butyl ketipinate H2L2 (1) with 2 N potassium hydroxide and reaction of the dianion (L2)2- with copper(II) chloride in methanol afforded the MC ether sandwich complex [(Kc Cu3(L2)3]2)OMe] (3) with a K/MC = 1 2 stoichiometry (Scheme 1, Fig. 1) [68, 69],... 

M-OH (metal hydroxide) Sodium hydroxide Potassium hydroxide Nucleophilic bases Deprotonation of organic acids with acidities as high as pKa = 16, hydrolysis of esters, amides, and nitriles... 

The catalytic approach to conjugate addition is illustrated by the addition of a (3-dike tone to an aromatic enone catalysed by potassium hydroxide and benzyltriethylammonium chloride, which is a phase transfer catalyst. Once again, the catalytic cycle is initiated by deprotonation of the most acidic component in the reaction mixture, acetyl acetone, which is followed by a cycle of conjugate addition and proton exchange leading inexorably to the product. 

The direct synthesis of a.g-unsaturated nitriles can be accomplished by treating the appropriate carbonyl compound with potassium hydroxide in acetonitrile.8 In order for direct condensation to succeed, acetonitrile must be deprotonated by the relatively weak base potassium hydroxide and the carbanion thus formed must add to the carbonyl. The cyanohydrin is presumably... 

Treatment of the latter by dilute potassium hydroxide solution gives the 2,6-diphenyl-4-methyl-4-terf-butyl-4i/-l,3,5-oxadiazine 120 in 71% yield. The formation of 120 is ascribed to a polar [4 + 2] cycloaddition7,40 of benzonitrile and the iV-acyliminium intermediate 118. However, after heating the reaction mixture of the three components mentioned above at 100°C for 10 min or a solution of the salt 119 in benzonitrile under the same conditions, the same product 121 is precipitated. Its deprotonation leads to 2-phenyl-4,4,5,5-tetramethyl-2-oxazoline 12285 (equation 41). 

The optimal base for closure to epoxide 2 is sodium ethoxide in ethanol, as potassium hydroxide in ethanol, sodium or potassium carbonate in ethanol, or benzyllrimethylammonium hydroxide in ethanol resulted in the formation of a complex mixture of decomposition products arising mainly from deprotonation at carbon. 

Horner-Wittig modification Alternatively, phosphine oxide reacts with aldehydes in the presence of a base (sodium amide, sodium hydride or potassium t-butoxide) to give an alkene. The phosphine oxide can be prepared by the thermal decomposition of alkyl-triphenylphosphonium hydroxide. Deprotonation of phosphine oxide with a base followed by addition to aldehyde yields salt of (3-hydroxy phosphineoxide, which undergoes further syn-elimination of the anion Ph2P02. The lithium salt of (3-hydroxy phosphineoxide can be isolated, but Na and K salt of (3-hydroxy phosphine oxide undergoes in situ elimination to give alkene (Scheme 4.26). 

Imidazole alkylations can be carried out under a variety of reaction conditions. For conventional iV-alkylations which are unlikely to be complicated in terms of regiochemistry, it is preferable to alkylate the imidazole anion (an Se2cB process). Such reactions are faster, higher yielding and less prone to azole salt formation than those in neutral conditions. The anion is generated best by the use of sodium in ethanol or liquid ammonia, with sodium or potassium hydroxide or carbonate, or by use of sodium hydride in dry DMF [3]. Addition of the alkylating agent to the deprotonated substrate completes the reaction. 

THE DEPROTONATION OF WEAK ACIDS WITH POTASSIUM HYDROXIDE APPLICATIONS TO THE SYNTHESIS OF ORGANOMETALLIC COMPOUNDS... 

Potassium hydroxide may be used to deprotonate extremely weakf acids if hydroxylic solvents such as water and alcohols are avoided The following sjmtheses illustrate the general applicability of this procedure to organometallic syntheses. 

Deprotonation of Weak Acids with Potassium Hydroxide 115... 

The anion Mo(CO)3C5H5 has been prepared by the reaction of the cyclopentadienyl anion with molybdenum hexacarbonyF- and by the reaction of dicyclopentadiene mth molybdenum hexacarbonyl to form [CoH5Mo(CO)3]2, followed by reduction of the latter compound with sodium amalgam. In view of the simplicity of preparing cyclopentadienylpotassium (by deprotonation of cyclopentadiene with potassium hydroxide), the former method is preferable, and is described below. The Mo(CO)3C6H5 anion may be converted to the hydride HMo-... 

This is the first volume of Inorganic Syntheses that has a special section (Chap. 1) devoted to syntheses of compounds that are of particular interest in the solid state. We hope that more syntheses of this type will appear in future volumes. This volume is also notable for the inclusion of reliable methods for preparing certain coordination compounds which are presently of great interest because of their catalytic activity. (See S3Titheses 18, 19, and 20.) Another unique feature is Chap. 4, which is devoted entirely to organometallic syntheses that illustrate the use of potassium hydroxide as a deprotonating agent. 

A lot of progress in this area is due to the work of Trost, who introduced diphenylsulphonium cyclopropylide and phenylthiocyclopropyl lithium as extremely versatile C3-building blocks. The first reagent is easily available from the corresponding sulphonium salt by deprotonation with suitable bases (either under irreversible conditions with dimsyl sodium, or, preferably, in a reversible manner by employing potassium hydroxide in DMSO). The ylide adds to a,) -unsaturated carbonyl compounds forming... 

Phenacylmethyl(dimethyl)selenonium bromide is far more acidic than the selenonium salts presented above since deprotonation can be achieved with aqueous potassium hydroxide (Scheme 68). The resulting ylide is stable at room temperature and decomposes to 1,2,3-triphenacylcyclopropane on irradiation or heating (Scheme 68, a). It reacts with benzalacetophenone in a different manner from methylene(dimethyl)selenurane (Scheme 59, c) and provides, rather than the oxirane, l-phenyl-2,3-phenacy(cyclopropane in very high yield (Scheme 68, b). ... 

---