Alcohol activation

Ammonium sulfide, 3, n Ammonium thiocyanate, 7, 48 Ammonolysis, 4, 3 7, 16 o-Amyl alcohol, 1, 4, 10 Amyl alcohol, active, 7, 77 mo-Amyl Bromide, 1,1, 2, 4, 10 w-Amyl Methyl Ketone, 7, do -Amyl propiolic acid, 7, 62 Analysis of Benzoylhydroperoxide, 8,32 Analysis of Benzoylperoxide, 8, 31 Anhydro-o-Hydroxymercoribenzoic Acid, 7, 3... 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

Opiates produce more discreet inhibitory effects since they bind to and activate inhibitory opioid receptors which, due to their restricted distribution, cause less widespread effects than those of the barbiturates and alcohol. Activation of the opioid receptors leads to a decrease in release of other neurotransmitters (glutamate, NA, DA, 5-HT, ACh, many peptides, etc.) and direct hyperpolarisation of cells by opening of K+ channels and decreasing Ca + channel activity via predominant actions on the mu opiate receptor (see Chapter 12). 

AtCCD7 (Schwartz et al. 2004). Organic solvent addition (dioxane, DMSO, methanol or acetone) improved activity under low concentrations (Mathieu et al. 2007). Short chain aliphatic alcohols activated the enzymes although the reason for this activation is unclear (probably due to influences on substrate accessibility or micellar structure). An increase in activity was observed for all aliphatic alcohols tested, although the optimal concentration lessened with increasing log P values (Schilling etal. 2007). 

A. Berkessel and J. A. Adrio, Dramatic acceleration of olefin epoxidation in fluorinated alcohols Activation of hydrogen peroxide by multiple H bond networks. J. Am. Chem. Soc. 128, 13412 13420 (2006). 

Asymmetric introduction of azide to the a-position of a carbonyl has been achieved by several methods. These include amine to azide conversion by diazo transfer,2 chiral enolate azidation,3 and displacement of optically active trifluoromethanesulfonates,4 p-nitrobenzenesulfonates,5 or halides.6 Alkyl 2-azidopropionates have been prepared in optically active form by diazo transfer,2 p-nitrobenzenesulfonate displacement,5 and the Mitsunobu displacement using zinc azide.7 The method presented here is the simplest of the displacement methods since alcohol activation and displacement steps occur in the same operation. In cases where the a-hydroxy esters are available, this would be the simplest method to introduce azide. 

This was overcome by acetylation of the same triol intermediate, using Novozym 435 (rmmobihzed CALB) in vinyl acetate and acetonitrile, to afford the monoacetate in 95 % yield and 97 % diastereoselectivity (Scheme 1.46). The monoacetate was then readily converted to the desired c -THF derivative by alcohol activation and cyclization as described above. 

Scheme 29 Allylic substitution with linear allylic alcohols activated by Lewis acids...

Example 9 a noteworthy example is the activation of bis(4-nitrophenyl)-iV,N-diisopropylphosphoroamidite [31] in coupling with alcohols activated by TMCS. This difunctional phosphitylating reagent does not react with alcohols in the presence of tetrazole, but in the presence of TMCS such a coupling becomes possible [37a,bj. 

Dramatic Acceleration of Olefin Epoxidation in Fluorinated Alcohols Activation of Hydrogen Peroxide by Multiple Hydrogen Bond Networks... 

Tertiary alcohols are rather inefficient in alkene/CO copolymerisation as the formation of alkoxy palladium complexes is less favored for them than for primary and secondary alcohols, while the lack of p hydrogens does not allow the formation of Pd-H. Some primary alcohols activated by electron-withdrawing substituents, e. g., CF3CH2OH, are equally unable to form Pd-H due to their low propensity to oxidation [6c]. 

The principle of alcohol activation by Bi(III) salts was first described by Dubac and colleagues in 1994 [35]. They reported a BiCl3-catalyzed transformation of various activated alcohols, including ferf-butyl, allyl and benzyl alcohols, to the corresponding chlorides by employing chloromethylsilane as a chlorinating agent (Scheme 4) [35]. 

For ethers of higher alcohols, activity comparable to that of dimethylether is observed with the [Ru(00) 13] catalysts, where simple carbonylation is favoured over homologation ( 1). ... 

Liquid in gel during drying water alcohol (% %) Activity (gg 0.5 hr1) Volume (cc g ) inside pores of diameter ... 

As activated DMSO and activated alcohols have a certain acidity, a prolonged alcohol activation before the addition of base may cause decomposition of very acid-sensitive functionalities. 

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