Allyl bromide Ammonium formate

Carbanions, generated by the reaction of benzylsilanes with tetra-n-butylammo-nium fluoride react with non-enolizable aldehydes to produce the alcohol [67], When a stoichiometric amount of the ammonium fluoride is used, the methylarene corresponding to the benzylsilane is frequently a by-product and arises from formation of the hydrogen difluoride salt during the reaction. When only catalytic amounts of the ammonium fluoride initiate the reaction, the formation of the methylarene is suppressed. In a similar type of reaction (although the mechanism is not known) between aldehydes and ketones, allyl bromide, and tin in the presence of trimethylsilyl chloride the yield of the but-l-en-4-ol is raised significantly by the addition of tetra-n-butylammonium bromide, particularly in the reactions with... 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

A valuable part of the [2,3]-sigmatropic rearrangement of ammonium ylides is the fact that stereochemical information can be transferred. For example, Kaiser and co-workers stereoselectively alkylated the C-6 position of penicillin using the nitrogen ylide 46 derived from lactam 45.28 Quatemization of 45 with allyl bromide followed by ylide generation using sodium hydride effected the [2,3]-rearrangement. This resulted in the exclusive formation of P-lactam 47 in 75% yield. 

Schiff base 52 in one-pot under mild phase-transfer conditions. For example, the initial treatment of a toluene solution of 52 and (S,S)-32e (1 mol%) with allyl bromide (1 equiv.) and CsOHH20 at —10 °C, and the subsequent reaction with benzyl bromide (1.2 equiv.) at 0 °C, resulted in formation of the double alkylation product 53 in 80% yield with 98% ee after hydrolysis. Notably, in the double alkylation of 52 by the addition of the halides in reverse order, the absolute configuration of the product 53 was confirmed to be opposite, indicating intervention of the chiral ammonium enolate 54 at the second alkylation stage (Scheme 4.17) [50]. 

Scheme 3 Reagents, (a) Allyl bromide/Acetone followed by optical resolution (b) Benzyl chloroformate, NaHC03 (aq), CHC13(98%) (c) Pd/C, H20, AcOH (100%) (d) di-tert-butyl dicarbonate, CH2C12 (98%) (e) Pd/C, Ammonium formate, MeOH (97%) (f) Allyl bromide, K2CQ3, Acetone (98%) (g) TFA, Triethylsilane, CH2C12(89%) (h) Pd/C, H2Q, AcOH [60]...

Since the observation that allylation of carbonyl compounds could be mediated by tin in aqueous medium [77], there has been an intensive development of the Barbier-type allylation reaction in water. Three metals were particularly investigated zinc, tin, and indium. In the aqueous zinc-promoted allylation, allylzinc species are considered unlikely. The initiation of the reaction could be attributed to the formation of an allylic radical anion on the metal surface this radical surface could then react with the carbonyl compound to give an alkoxide radical, which could add an electron and form the alcohols [82]. Allyl bromide or even chloride reacts with aldehydes and ketones in the presence of commercial zinc powder in a mixture of tetrahydrofuran and saturated ammonium chloride aqueous solution (Eq. 7) [83]. 

Many aspects of the regioselective manipulation of polyols through dialkylstannylene acetals have been studied and some interesting modifications have improved this procedure [53, 55], For example, the regioselective formation of monobenzyl, monoallyl and monomethyl ethers, which normally proceeds at very slow speed, is markedly enhanced when the reaction of benzyl and allyl bromides or methyl iodide on dialkylstannylene derivatives of polyhydroxy compounds is carried out in the presence of stoichiometric amounts of quaternary ammonium halides [37,56,57]. Several examples of this modified procedure, such as the regioselective mono-O-alkylation of disaccharide glycosides (Scheme 2), have been reported [58]. 

Hendrickson synthesized allyl triflones using tetrabutylam-monium triflinate. The quaternary ammonium system is more soluble and 20-40 times more reactive than the conventional potassium triflinate. Tetra-n-butylammonlum azide (6) prepared from tetra-/3-butylammonium hydroxide and sodium azide reacts with triflic anhydride in chloroform at —78°C to give a 1 1 mixture of tetrabutylammonium triflinate (7) and tetrabutyl-ammonium triflate (8). Treatment of this mixture with allyl bromide gives the corresponding allyl triflone (5) in almost quantitative yield. The water-soluble triflate coproduct (8) in the reaction mixture does not interfere with the formation of (5), which is readily Isolated (eq 4). 

When thien-2-ylacetic acid was subjected to the abovementioned reaction coti-ditions, similar ring opening was observed and the products consisted of (Z)-3-benzylthio-3-hexenoic acid and (Z)- and ( )-3-benzylthio-2-hexenoic acid with the ratio of 84 12 4. As illustrated in Scheme 127, the Birch reduction of 2-(thien-2-yl) propanoic acid with five equivalents of sodium in liquid ammonia in the presence of ethanol and a subsequent treatment with ammonium chloride and benzyl bromide led to the formation of (Z)-3-benzylthio-2-methyl-3-hexenoic acid in the yield of 63%. Additionally, under similar reaction conditions, 2-(thien-2-yl)hexenoic acid and 2-(thien-2-yl)-4-pentenoic acid also created the corresponding (Z)-3-benzylthio-2-butyl-3-hexenoic acid and (Z)-2-allyl-3-benzylthio-3-hexenoic acid with 77 and 76% yields, respectively [140]. 

Tertiary amines are also known to effect the phase transfer addition of cyanide ion to primary, allylic, and benzylic halides [9]. The reported effect of amine structure on catalytic efficiency closely parallels that reported by Hennis for ester formation in a two-phase system (see Sect. 1.7). Both the nitrogen of the amine and the carbon bearing halide of the alkyl bromide must be sterically accessible for the reaction to succeed. Thus, -hexylamine is effective in concert with -butyl bromide but the combinations of either 5-butyl bromide and -hexylamine or -butyl bromide and cyclohexylamine are not. Tertiary amines are generally more effective than secondary or primary amines. In addition, the yields of primary nitriles decrease dramatically with the size of the primary alkyl bromide from quantitative with n-butyl to only 6% with -decyl bromide when -hexylamine is used as phase transfer catalyst. On the other hand, tributylamine was equally useful as a catalyst for the quantitative conversion of either 1-bromohexane or 1-bromodecane to the corresponding nitriles [9]. In general, these observations accord with those of Hennis and coworkers indicating that this reaction is an example of in situ formation of and catalysis by quaternary ammonium salts [10]. 

When carried out with ( )-rich l-bromo-2-butene in THF/H2O solution, the SnCla Barbier-type allylation of aldehydes provided homoallylic alcohols, mainly with the anti configuration. By contrast, syn allylation occurred with tin(ll) iodide (Scheme 4.1). The syn-selectivity, suggesting an acyclic antiperi-planar transition state, was even improved by the addition of tetrabutyl-ammonium bromide in the aqueous medium. This enhancement of selectivity could be explained by the formation of a pentacoordinated tin species, preventing the tin atom from coordinating the oxygen atom of the aldehyde (Masuyama el a/., 1996). 

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