Tetrabutylammonium alkoxides

In the cyclization of the corresponding cis-epoxides, with the aim of obtaining the corresponding cis-2,3-disubstituted tetrahydropyrans, a similar trend was observed. For these systems, however, the 6-endo pathway was less favored, which was ascribed to difficulties in attaining a TS conformation that would allow for maximum stabilization of the developing p-orbital with the adjacent 7t-system. Alternatively, palladium-catalyzed cyclization of the tetrabutylammonium alkoxide derived from 33b results in the corresponding ris-2,3-disubstituted tetrahydro-pyran in excellent yield and selectivity (90%, dr >99 1), while the ris-epoxide gives stereoisomer 37b (86%, dr 98 2) [112]. 

Haggard and Lewis have shown that tetrabutylammonium alkoxides polymerize methacrylates in alcohol solution [68]. Block polymer synthesis is not possible since the ester groups on the monomer exchange with the solvent. 

Nucleophilic attack at carbon atoms is quite common and usually results in opening of the heterocycle. Among the most typical types of substrate, one finds 1,2,3-oxathiazines. For example, in the nucleophilic addition of tetrabutyl-ammonium fluoride (TBAF) to 1,2,3-oxathiazine 103, the tetrabutylammonium alkoxide intermediate 104 reacts intramolecularly to give 3-aminotetrahydrofuran 105 <20050BC603>. Substrate 103 undergoes similar nucleophilic additions with morpholine and phenylthiolate to afford derivatives 106 and 107 (Scheme 9). 

The success of the reaction depends on the preferential extraction of tetrabutylammonium alkoxide rather than the corresponding hydroxide salt. The preference of the quaternary ammonium ion for alkoxide over hydroxide can be attributed to two factors. First, the soft (larger, more polarizable) quat prefers to pair with the soft (larger, more polarizable) alkoxide rather than the hard hydroxide ion. Second, hydroxide is more effectively solvated by the aqueous medium than is the alkoxide and prefers to remain in that phase. Under phase transfer conditions, secondary alcohols react more slowly than do primary alcohols, probably due to the lower acidity of secondary alcohols or to steric factors. 

Very recently Lubineau et al. also accomplished stereoselective synthesis of a-and P-glycosides [11]. Allylation of acetylated GIcNAc (34) with ally bromide in the presence of NaH in CH2CI2 gave the p-anomer (37b) exclusively. In contrast, addition of BU4NI to the reaction mixture gave an a-glycoside (37a) only. This complete stereoselectivity is because the anomeric tetrabutylammonium alkoxide was... 

Similar procedures adopted for the synthesis of TS-1 (the mixed alkoxide method, dissolved titanium method, pre-hydrolysis method, wetness impregnation method, and promoter induced synthesis method) were also used for the synthesis of TS-2. Tetrabutylammonium hydroxide (TBAOH) instead of TPAOH was used as the template (6,7,305-308). 

Other indoles that have been prepared using the Sonogashira coupling and cyclization sequence include 5,7-difluoroindole and 5,6,7-trifluoroindole [219], 4-, 5-, and 7-methoxyindoles and 5-, 6-, and 7-(triisopropylsilyl)oxyindoles [220], the 5,6-dichloroindole SB 242784, a compound in development for the treatment of osteoporosis [221], 5-azaindoles [222], 7-azaindoles [160], 2,2-biindolyls [223,176], 2-octylindole for use in a synthesis of carazostatin [224], chiral indole precursors for syntheses of carbazoquinocins A and D [225], a series of 5,7-disubstituted indoles [226], a pyrrolo[2,3-eJindole [226], an indolo[7,6-g]indole [227], pyrrolo[3,2,l-y]quinolines from 4-arylamino-8-iodoquinolines [228], optically active indol-2-ylarylcarbinols [229], 2-alkynylindoles [176], 7-substituted indoles via the lithiation of the intermediate 2-alkynylaniline derivative [230], and a variety of 2,5,6-trisubstituted indoles [231], This latter study employs tetrabutylammonium fluoride, instead of Cul or alkoxide, to effect the final cyclization of 215 to indoles 216 as summarized here. 

Theory would predict that PTC should be useful in increasing the alkylation efficiency of hydrophobic electrophiles with cellulose ether alkoxides. However, there is very little previous work reported in using PTC in the preparation of cellulose ethers. Daly and coworkers10 reported that quaternary ammonium salts were useful in catalyzing the heterogeneous benzylation of cellulose, but when we applied this technique to the DPGE alkylation of nascent HEC in aqueous /-butyl alcohol, the presence of catalytic amounts of tetramethylammonium chloride or tetrabutylammonium bromide actually afforded lower alkylation efficiencies. 

Oxolane [66-69], 1,4-dioxane [70] or, eventually, an excess of benzyl bromide [71] or chloride [72, 73] are the solvents of choice complementing the dipolar aprotic solvents mentioned above. A catalytic effect of tetrabutylammonium iodide has been observed [66, 69] for this reagent system 1,2 5,6-di-O-isopropylidene-ot-D-gluco-furanose needs 24 h boiling with excess benzyl bromide and sodium hydride in oxolane for complete benzylation of the hindered secondary hydroxyl group, but 165 min at 20 °C are sufficient when 0.01 equiv. of the catalyst is present. Ion-pair formation is probably responsible for the increase of the alkoxide reactivity [66]. 

The sodium or potassium alkoxide prepared from primary and secondary alcohols and sodium hydride or potassium hydride in THF reacts with 2-(trimethyl-silyi)ethoxymethyl chloride (SEMCl, bp 57-59 PC/1 kPa, HAZARD carcinogenic) to give the SEM ethers in good yield [Scheme 4.304]481 Alternatively, the alcohol can be alkylated with SEMC1 in the presence of f-PrjNEt in dichloro-methane at 4013 C [Scheme 4.305].257,525,555 Conversion of the SEMCl to the corresponding iodide in situ using tetrabutylammonium iodide accelerates the reaction ... 

The tin-mediated strategy was applied to my o- and chiro-inositol. Thus, treatment of myo-inositol with 5 equiv of dibutyltin oxide and allyl bromide in the presence of tetrabutylammonium bromide furnished two major tetraallylated products 119 and 120. Parallel results were obtained when crotyl bromide was used. When 3 equiv of the tin oxide were used, 1,3,4-triallyl ether 121 was a major product (Scheme 3-18).57 Five membered cyclic stannylene derivatives like 123 may be formed predominantly at the 1,2-cis-diol site and then the more reactive alkoxide reacts with an electrophile, as is shown in Scheme 3-18.58... 

Electrosynthesis by anodic dissolution of the metal in absolute alcohol appears for many elements to be a promising, inexpensive way to obtain large amounts of metal alkoxides [54]. The process goes smoothly and has good current yields for metals, such as scandium and lanthanides, and early transition metals (Ti, Zr, and Nb) using tetrabutylammonium bromide as an electrolyte. Oxo or hydroxo compounds are obtained for more electropositive metals (Mg and alkaline-earth metals), however, probably as a result of alcohol dehydration reactions. 

PEO-PSt-PBd-PEO tetrablock terpolymer was prepared by a multistep anionic polymerization method. First, an a,0-hydroxy PSt-Z -PBd was synthesized, using the protected initiator TBDMS and sequential monomer addition of St and Bd. The reaction was terminated by EO. After deprotection with tetrabutylammonium fluoride (TBAF), both OH ends were converted to potassium alkoxides and used to polymerize EO (Scheme 10). Depending on the length of the outer PEO segments, these ABCA amphiphilic terpolymers form vesicles or worm-like micelles in water. 

TiCl4 in oxygen [11], hydrolysis of titanium alkoxides in different conditions [12], photo-assisted sol-gel method from titanium tetrabutoxide [13], hydrothermal oxidation of metallic titanium powder [14], hydrothermal hydrolysis of titanium tetraethoxide [15], oxysulfate [16,17] and tetrabutylammonium [18], solvothermal synthesis from titanium butoxide in 2-butanol [19], crystallization of amorphous Ti02 in hydrothermal condition [20], vapor hydrolysis of titanium tetraisopropox-ide [21], destabilization of titanium lactate [22], decomposition of titania-hydrate [23], epoxide sol-gel process to aerogel of Ti02 [24], hydrolysis of aqueous solution of TiCl4 in the presence of polyethyleneglycol [25], and so forth. 

It remains to be mentioned that contrary to what we believed together with others, the solutions of quaternary alkoxides appear to be quite stable at room temperature when well protected from carbon dioxide and humidity. We kept solutions of tetrabutylammonium ethoxide or iso-propoxide in ethanol—benzene 1 10 in automatic burets at 25 to 30°C during a rather humid summer season and after two months they were practically unchanged, giving the same titration curves as before. 

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