2,4,6 Collidine

The criterion has also been applied qualitatively. Thus, 2,4,6-collidine and 1,2,4,6-tetramethylpyridinium cation can be nitrated under identi-... 

For this series of compounds qualitative information is quite extensive. Application of the criteria discussed in 8.2, in particular comparison with the corresponding methyl quaternary salt, establishment of the rate profile for nitration in sulphuric acid, and consideration of the encounter rate and activation parameters, shows that 2,4,6-collidine is nitrated as its cation. The same is true for the 3-nitration of 2,4- ... 

Ph3CCl, 2,4,6-collidine, CH2CI2, Bu4N" C104, 15 min, 97% yield. This is an improved procedure for installing the trityl group on polymer-supported nucleosides. 

Hg(C104)2, 2,4,6-collidine, acetone, H2O (9 1), 5 h NH3, dioxane, H2O (1 1). In this case Hg(II) is used to cleave the MTM group, liberating a hydroxyl group, which assists in the cleavage of the carbonate on treatment with ammonia. Cleavage by ammonia is 500 times faster for this hydroxy derivative than for the initial MTM derivative. 

Chrysene, 46, 95 Cinnamaldehyde, 46, 36 reaction with hydrazine, 47, 99 2,4,6-Collidine in hydrolysis of esters to acids, 46, 8... 

By following the reported procedure, coupling reaction of 86 with 2,3,4-tri-0-benzoyl-a-L-arabinopyranosyl bromide in the presence of AgOTf and 2,4,6-collidine gave the coupled product (88) in 57% yield. Finally, treatment of 88 with NaOMe in MeOH provided the synthetic geranyl 6-0-a-L-arabinopyranosyl-P-D-glucopyranoside (Kenposide A, 83) in 85% yield. 

Catalytic turn-over [59,60] in McMurry couplings [61], Nozaki-Hiyama reactions [62,63], and pinacol couplings [64,65] has been reported by Fiirst-ner and by Hirao by in situ silylation of titanium, chromium and vanadium oxo species with McaSiCl. In the epoxide-opening reactions, protonation can be employed for mediating catalytic turn-over instead of silylation because the intermediate radicals are stable toward protic conditions. The amount of Cp2TiCl needed for achieving isolated yields similar to the stoichiometric process can be reduced to 1-10 mol% by using 2,4,6-collidine hydrochloride or 2,6-lutidine hydrochloride as the acid and Zn or Mn dust as the reduc-tant (Scheme 9) [66,67]. 

The above-mentioned results indicate the additive effect of protons. Actually, a catalytic process is formed by protonation of the metal-oxygen bond instead of silylation. 2,6-Lutidine hydrochloride or 2,4,6-collidine hydrochloride serves as a proton source in the Cp2TiCl2-catalyzed pinacol coupling of aromatic aldehydes in the presence of Mn as the stoichiometric reduc-tant [30]. Considering the pKa values, pyridinium hydrochlorides are likely to be an appropriate proton source. Protonation of the titanium-bound oxygen atom permits regeneration of the active catalyst. High diastereoselectivity is attained by this fast protonation. Furthermore, pyridine derivatives can be recovered simply by acid-base extraction or distillation. 

As in the reductive ring-opening, titanocene—oxygen bonds have to be protonated. Here, a titanium enolate, which is generated after reductive trapping of an enol radical, has to be protonated, in addition to a simple titanocene alkoxide. As before, 2,4,6-collidine hydrochloride constitutes a suitable acid to achieve catalytic turnover, but here zinc dust turned out to be the reductant of choice [31c], The features of the stoichiometric reaction are preserved under our conditions. Acrylates and acrylonitriles are excellent radical acceptors in these reactions. Methyl vinyl ketone did not yield the desired addition product. Under the standard reaction conditions, a-substituted acceptors are readily tolerated, but (3-substitution gives the products only in low yields. 

Cyclobutanones (11, 560-561). Ketenimium salts are more reactive than ke-tenes in [2 + 2] cycloadditions with alkenes to prepare cyclobutanones. The salts are readily available by in situ reaction of tertiary amides with triflic anhydride and a base, generally 2,4,6-collidine. The cycloaddition proceeds satisfactorily with alkyl-substituted alkenes and alkynes, but not with enol ethers or enamines.1... 

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