Tetrabutylammonium iodide TBAI

Current single-mode continuous-flow microwave reactors allow the processing of comparatively small volumes. Much larger volumes can be processed in continuous-flow reactors that are housed inside a multimode microwave system. In a 2001 publication, Shieh and coworkers described the methylation of phenols, indoles, and benzimidazoles with dimethyl carbonate under continuous-flow microwave conditions using a Milestone ETHOS-CFR reactor (see Fig. 3.11) [104]. In a typical procedure, a solution containing the substrate, dimethyl carbonate, 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) base, tetrabutylammonium iodide (TBAI), and a solvent was circulated by a pump through the microwave reactor, which was preheated to 160 °C and 20 bar by microwave irradiation (Scheme 4.31). Under these condi-... 

In the presence of tetrabutylammonium iodide (TBAI) in its adsorption region on the pc-Zn electrode, the edl capacitance decreased with increasing TBAI concentration and the capacity minimum shifted to more negative potentials [13]. At still more negative potentials, a well-defined adsorption- desorption peak was observed. Splitting of this peak was explained by the presence of different faces on the surface of pc-Zn electrode. 

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]. 

As an improved method, the combination of cesium carbonate and tetrabutylammonium iodide (TBAI) is used as a base in DMF (eq 19). The cesium salts (28) are formed by treating (25) with CS2CO3 and TBAI at 23 °C for 1 h. The use of other alkali metal carbonates gives the corresponding salts in lower yields on the basis of their trapping with benzyl bromide. TBAI is also crucial in the reaction. The reaction in the absence of TBAI is less effective. A variety of alkyl halides such as primary and secondary alkyl bromides are used for the alkylation of the salts (28). With isoleucine bromide as electrophile, the nucleophilic substitution reaction with the salt (28) proceeds with retention of configuration. 

The cohesive force between cellulosic fibers from Kraft bleached pulp was also measured in solutions of a cationic surfactant, tetrabutylammonium iodide (TBAI). The cohesive force, p, as a function of the concentration of TBAI is shown in Figure 2.25. As seen in this figure, the cohesive force undergoes a sharp decrease as the TBAI concentration increases and then passes through a... 

To a stirred solution of tetrabutylammonium iodide (TBAI, 0.2 mmol) in dry dichloromethane (5 mL) at -78 °C was added titanium tetrachloride (1.5 mmol) dropwise. After stirring for two minutes, a mixture of the enone 142 (1 mmol) and p-nitrobenzaldehyde (2 mmol) in dry dichloromethane (5 mL) was added. The reaction mixture was slowly warmed to -30 C and kept at this temperature for 8 h. A saturated aqueous solution of sodium bicarbonate was added, followed by filtration through a celite pad. The organic layer from the filtrate was separated, and the aqueous layer was extracted with ethyl acetate. The combined organic layers were washed with brine, dried over sodium sulfate, filtered, and concentrated. The crude product was then purified by column chromatography eluting with hexane ethyl acetate (80 20) to deliver the product 143 as an oil in 85% yield. 

Most recently, Zhdankin described that the combination of catalytic amounts of tetrabutylammonium iodide (TBAI) with m-chloroperoxybenzoic acid (mCPBA) as a terminal oxidant [77] was the effective catalyst system for the aziridination of various types of alkenes (Scheme 2.53) [78]. The reaction of styrenes with either electron-donating or electron-withdrawing groups afforded the desired aziridines in good yields. Cyclic alkenes and aliphatic alkenes such as 1-decene... 

After taking up the challenge for the synthesis of (5)-metolachlor on an industrial scale, Blaser reported on the very first example of asymmetric reductive amination and succeeded to synthesize the desired (5)-enantiomer of metolachlor 77 up to 78% ee ° Blaser optimized the reaction condition where the 2-methyl-5-ethylaniline (MEA, 79) was treated with 1.2 equivalents of dry methoxyacetone (MOA, 78), 0.01 mol% Ir-xyliphos catalyst 81 in the presence of tetrabutylammonium iodide (TBAI), and a small amount of trifluoroacetic acid in cyclohexane as the solvent under 80 bar hydrogen pressure at 50 °C. Within 16 hours, almost complete conversion was reached furnishing the chiral amine 80 with 99% conversion and 78% ee. Upon chloroa-cetylization, 80 afforded the desired compound metolachlor 77 without any loss of enantioselectivity (Scheme 39.20). 

---