2,4-Lutidine metallation

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. 

A 1-1. three-necked flask is fitted with a dry ice-acetone condenser, a glass stirrer, and a glass stopper (Note 1). Potassium amide is prepared in 400 ml. of liquid ammonia from 8.0 g. (0.20 g.-atom) of potassium metal (Note 2). The glass stopper is replaced with an addition funnel containing 32.1 g. (0.300 mole) (Note 3) of 2,(>-hitidine dissolved in about 20 ml. of anhydrous ether. The lutidine solution is added to the amide... 

Ethyl pyridine-2-acetate and ethyl 6-methylpyridine-2-acetate have previously been prepared by carboxylation of the lithio derivatives of a-picoline and lutidine, respectively. Use of ethyl carbonate to acylate the organometallic derivative avoids the intermediacy of the (unstable) carboxylic acid, and the yields are better. In the present procedure potassium amide is used as the metalating agent the submitters report that the same esters may be formed by metalation with sodium amide (43% yield) or with w-butyllithium (39% yield). The latter conditions also yield an appreciable amount of the acid (which decarboxylates). 

N-Do/Jor Ligands. The full account of the preparation and properties of V[N(SiMc3)2]3 has been published. (Et4N)3[V(NCSe)e] has been prepared and its electronic spectrum reported in several solvents. The electronic spectra of fVL lfNCSij complexes (L = py, 3-picoline, 3,4-lutidine, or 3,5-lutidine) are consistent with tetrahedral microsymmetry about the V " atom, and the magnetic properties of V complexes with the thiosemicarbazones of salicylaldehyde and pyruvic acid have been interpreted in terms of a tetragonal environment about the metal. ... 

More recent reports from Cordova [155] and Wang [156] have described the cyclopropanation of a, P-unsaturated aldehydes 99 with diethyl bromomalonates 100 and 2-bromo ethyl acetoacetate catalysed by a series of diaryIprolinol derivatives. Both describe 30 as being the most efficient catalyst in many cases and optimal reaction conditions are similar. Some representative examples of this cyclopropanation are shown in Scheme 40. The transformation results in the formation of two new C-C bonds, a new quaternary carbon centre and a densely functionalised product ripe for further synthetic manipulation. Triethylamine or 2,6-lutidine are required as a stoichiometric additive in order to remove the HBr produced during the reaction sequence. The use of sodium acetate (4.0 equivalents) as an additive led to subsequent stereoselective ring opening of the cyclopropane to give a,P-unsaturated aldehydes 101. It can be envisioned that these highly functionalised materials may prove useful substrates in a variety of imin-ium ion or metal catalysed transformations. 

The asymmetric hydrogenation of unfunctionalized ketones is a much more challenging task than that of functionalized ketones [3 j, 115]. Many chiral catalysts which are effective for functionalized ketones do not provide useful levels of enantioselectivity for unfunctio-nalized ketones, due to a lack of secondary coordination to the metal center. Zhang demonstrated the enantioselective hydrogenation of simple aromatic and aliphatic ketones using the electron-donating diphosphane PennPhos, which has a bulky, rigid and well-defined chiral backbone, in the presence of 2,6-lutidine and potassium bromide [36]. 

Scheme 13.15 Preparation of oxygen-substituted VCPs 142 (Eq. 1) and 163 (Eq. 2). Conditions (a) Na metal, TMSCI, Et20, A (b) MeOH, RT (c) vinylmagnesium bromide, EtjO, 0°C to RT (d) TBSOTf, 2,6-lutidine, CHjCb, RT (e) N-bromo-succinimide, 2-methoxyethanol, -78 °C to RT (f) KOH, RT to 90°C (g) 1.3 equiv. CH2I2, Zn metal, CuCI, AcCI, EtjO, A.

Only for lutidine has this been confirmed, wherein the isomerizations occur with specific rate constants of >103 sec-1 (172— tj1) and 36 10 sec-1 (tj1 — r)2) for the Os(III) and Os(II) complexes, respectively. It is worth noting that the resulting complex, [Os(NH3)5(Af-2,6-lutidine) ]3+, cannot be made by conventional, substitution-based, synthetic methods for Os(III), and is likely to be the only reported example of this molecule bonding to a transition metal through nitrogen. 

Alternatively, Sasaki et al. [31] provided a glycosylation method using glycosyl bromide in the presence of hindered amines such as 2,6-lutidine or TMU under high-pressure conditions (O Scheme 1). In addition, Nishizawa et al. [32] developed a thermal glycosylation of glycosyl chloride in the presence of a-methylstyrene or TMU as an acid scavenger without any metal salts (O Scheme 2). 

Darr and Poliakoff conducted one of the first studies where SC-CO2 was used in a two-stage continuous reaction and purification process to form pure organo-metallic products. The ds-W(CO)4(pyridine)2 or novel c/ -W(CO)4(3,5 lutidine)2 were formed in a continuous flow reactor at 488 K and were then removed from solution via precipitation, with a second flow of CO2 used to remove the excess solvent and reactant for reclamation and recycle. The benefits of this system, aside from the production of novel materials, include reduction of organic solvent consumption, decrease in number of stages and time, and production of 100% purity product. 

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