Ambient anion alkylation

In a further development on this theme, the thiol, 153, is first alkylated to the corresponding benzyl ether (158). Treatment with sodium methoxide removes the proton on the amide nitrogen to afford the ambient anion (159). This undergoes alkylation with methyl bromide on the ring nitrogen thus it locks amide into the imine form (160). Chlorolysis serves both to oxidize the sulfur to the sulfone stage and to cleave the benzyl ether linkage there is thus obtained the sulfonyl chloride, 161. 

Enamines, like enolate anions, are ambient nucleophiles. Alkylation at nitrogen is sometimes a competing reaction. The product of A -alkylation, after hydrolysis, leads to recovery of starting ketone. 

Wherever possible, we have sought a direct comparison of the reactivities of structurally related Crni and q-II alkyls with ethylene. For example, after having established the catalytic activity of complexes of the type [( Cri (L)2R] (see above), we showed that the isostructural neutral compounds Cp Crn(L)2R did not polymerize ethylene instead facile P-hydrogen elimination was observed. [3) This difference in reactivity was not due to the charge of the complexes. Thus, we have subsequently shown that neutral Cr J alkyls are also active polymerization catalysts. For example, Cp Cr I(THF)Bz2 and even anionic Li[Cp Cr H(Bz)3] (Bz = benzyl) polymerized ethylene at ambient temperature and pressure, while the structurally related CpCrD(bipy)Bz proved inert.[5]... 

The most studied catalyst family of this type are lithium alkyls. With relatively non-bulky substituents, for example nBuLi, the polymerization of MMA is complicated by side reactions.4 0 These may be suppressed if bulkier initiators such as 1,1-diphenylhexyllithium are used,431 especially at low temperature (typically —78 °C), allowing the synthesis of block copolymers.432,433 The addition of bulky lithium alkoxides to alkyllithium initiators also retards the rate of intramolecular cyclization, thus allowing the polymerization temperature to be raised.427 LiCl has been used to similar effect, allowing monodisperse PMMA (Mw/Mn = 1.2) to be prepared at —20 °C.434 Sterically hindered lithium aluminum alkyls have been used at ambient (or higher) temperature to polymerize MMA in a controlled way.435 This process has been termed screened anionic polymerization since the bulky alkyl substituents screen the propagating terminus from side reactions. 

The extensive use of alkyllithium initiators is due to their solubility in hydrocarbon solvents. Alkyls or aryls of the heavier alkali metals are poorly soluble in hydrocarbons, a consequence of their more ionic nature. The heavier alkali metal compounds, as well as alkyllithiums, are soluble in more polar solvents such as ethers. The use of most of the alkali metal compounds, especially, the more ionic ones, in ether solvents is somewhat limited by their reactivity toward ethers. The problem is overcome by working below ambient temperatures and/or using less reactive (i.e., resonance-stabilized) anions as in benzylpotassium, cumylcesium and diphenylmethyllithium. 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

Inorganic bases have been also employed in this system. When Butcher first used alkali carbonates [50], it was reported that, in DMF and at ambient temperature, the carbamation of primary and secondary aliphatic amines (or also arylamines) with alkyl halides under a C02 atmosphere (0.1 MPa) was effectively promoted by Cs2C03 [50, 51]. The Cs+ cations in the solvent used (DMF) did not form ion pairs with counterions, and favored the formation of naked carbamate anions that were more reactive at the O-ends with alkyl halides. Jung further found that the addition of tetrabutylammonium iodide (TBAI) to the system RR NH/ C02/RX/Cs2C03/DMF promoted the carbamation process with a higher yield and selectivity with respect to N-alkylation [51]. The process has been successfully extended to the synthesis of carbamate functionalities on solid phases. In this case, resin-bound carbamates are readily released from the resin by treatment with LiAlH4 in THF, yielding the respective N-methyl secondary amines [51]. 

Coordination polymerisations of alkyl isocyanates have not been widely studied, since these monomers could be polymerised via their C=N bond by using anionic initiators. However, such anionic polymerisations require low-temperature conditions [264]. It has been found recently [265] that alkyl isocyanates are capable of polymerisation in the presence of coordination catalysts at ambient temperature. By contrast, phenyl isocyanate appeared capable of coordination copolymerisation with oxirane [266]. 

Separation science focuses on room temperature ionic liquids (RTlLs), salts that are liquid at ambient temperature. They have been studied as extracting solvents, stationary and mobile phases, mobile phase additives, and other uses. Common RTILs consist of a bulky nitrogen- or phosphorus-containing organic cation (pyridinium or pyrrolidinium, alkyl-imidazolium, ammonium or phosphonium) and a variety of organic and inorganic anions (triflate, dicyanamide, trifluoroacetate, acetate trifluo-romethylsulfate, nitrate, perchlorate, bromide, chloride, chloroaluminate, tetrafluo-roborate, hexafluorophosphate). 

Ethylammonium nitrate (entry 18 in Table 3-1) was shown in 1914 to have m.p. 12 °C and was hence the first room temperature ionic Hquid [156] this was followed in 1967 by tetra- -hexylammonium benzoate with m.p. —50 °C (entry 26) [169], Ambient-temperature ionic liquids based on l-alkyl-3-methylimidazolium salts (entries 19-24) were first reported by Wilkes et al. in 1982 as tetrachloroaluminates [162a], Replacement of this moisture-sensitive anion by the tetrafluoroborate ion and other anions led, in 1992, to air- and water-stable, room temperature ionic liquids [162b], which have since found increasing application as reaction media for various kinds of organic reactions, mainly owing to the work of Seddon [167, 190] and Hussey [187], Suitably selected... 

Alkynes from aldehydes or ketones. The reaction of the anion ef 1 with diaryl ketones, ArCOAr, to form alkynes, ArC=CAr, was reported first by Colvin and Hamill, but the method was said to fail or give low yield with substrates with enolizable hydrogens. Since then experimental details have been perfected, and the method has proved to be useful." The anion of 1 is prepared with potassium f-butoxide, and the reaction with the carbonyl compound is conducted for 12-16 hours at —78° before it is allowed to warm to the ambient temperature. Linder these conditions, alkynes can be obtained in 50-80% yield from aldehydes, diaryl ketones, and alkyl aryl ketones, but not from dialkyl ketones. The proposed mechanism is shown in equation (I). 

Carbonylferrate salts, such as K [HFe(CO)4] , which is readily prepared from [Fe(CO)s] and ethanolic KOH, react with alkyl bromides or iodides to form alkyliron complexes. Under ambient conditions these complexes undergo insertion of CO and, in the presence of excess CO, aldehyde is eliminated and [Fe(CO)s] is regenerated (Scheme 10). Unfortunately, the reaction is not catalytic and the hydridocar-bonylferrate salt must be prepared in a separate step. Using the commercially available salt Na2[Fe(CO)4] a similar reaction takes place, but in this case the intermediate acyl complex is anionic and acid treatment is necessary to liberate the aldehyde (Scheme 11). ... 

Coh(I)alamin is a powerful nucleophile, 40 000 times as reactive as the thiolate anion.Its intrinsic chemical reactivity as a nucleophile makes it an important species in the nonenzymatic synthesis of alkylcohalamins. Coh(I)alamin is easily alkylated at ambient temperatures by primary alkyl halides, alkenes, and alkynes. Secondary and tertiary alkyl halides either do not react or form unstable products because of steric crowding with the macrocyclic cobamide. Nonenzymatic alkylation by an alkyl halide is illustrated in Equation (6), where X is Cl, Br, or I. 

Cyclohexadienones can be considered structurally as hemi-quinones and they have been synthesised in recent years by a variety of simple approaches in which invariably a substituent becomes attached to the 2- or 4- position and the structure becomes locked. 2,6-Dimethylphenol in hexane or benzene converted at 0°C to the anion with n-butyllithium in hexane, gradually warmed to ambient temperature, stirred for 1 hour, and then alkylated at 0 C with chloromethyl methyl ether afforded after 2-4 hours reaction 2,6-dimethyl-... 

Sulfinate anions have been used as nucleophiles in palladium-catalyzed allylic alkylation [143]. More recently, both Cu- and Pd-catalyzed couplings of sulfinate anions with aryl halides have also been reported as a means to generate unsymmetrical diaryl sulfones, which are common motifs in bioactive molecules [38, 93, 144—148]. Similarly, Cu-catalyzed coupling of arylboronic acids with sulfinate anions has been reported [95,149,150]. Notably, Kantam and co-workers found that the use of ionic liquids permits Cu(OAc)2-catalyzed sulfone synthesis at ambient temperature and with convenient product separation and catalyst recyclability (17) [150]. 

The effects of increasing the concentration of initiator (i.e. increased conversion, decreased and broader PDi) and reducing the reaction temperature (i.e. decreased conversion, increased M and narrower PDi) for the polymerizations in ambient-temperature ionic Uquids are the same as observed in conventional solvents. Mays et al. reported similar results and, in addition, used NMR to investigate the stereochemistry of the PMMA produced in (BMIMjlPFej. They found that the stereochemistry is almost identical to that for PMMA produced by free radical polymerization in conventional solvents [28]. The homopolymerization and copolymerization of several other monomers are also reported. Similar to vdiat was found by Noda and Watanabe, in many cases the polymer was not soluble in the ionic liquid and thus phase separated [28,29]. Free radical polymerization of n-butyl methacrylate in ionic liquids based on imidazolium, pyridinium, and alkylammonium salts as solvents was investigated with a systematic variation of the length of the alkyl substituents on the cations, and employing different anions such as tetrafluoroborate, hexafluorophosphate, tosylate, triflate, alkyl sulfates and dimethyl phosphate [31]. 

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