Olefinic alcohols, oxidative esterification

Olefins add anhydrous acetic acid to give esters, usually of secondary or tertiary alcohols propjiene [115-07-1] yields isopropyl acetate [108-21-4], isobutjiene [115-11-7] gives tert-huty acetate [540-88-5]. Minute amounts of water inhibit the reaction. Unsaturated esters can be prepared by a combined oxidative esterification over a platinum group metal catalyst. Eor example, ethylene-air-acetic acid passed over a palladium—Hthium acetate catalyst yields vinyl acetate. 

Pincer-ligated iridium complexes have been used as homogeneous catalysts for the dehydrogenation of aliphatic polyalkenes to give partially unsaturated polymers. The catalyst appears to be selective for dehydrogenation in branches as compared with the backbone of the polymer.56 The mechanism shown in Scheme 1 has been suggested for an [IrCl(cod)]2-catalysed oxidative esterification reaction of aliphatic aldehydes and olefinic alcohols.57... 

The synthesis of the 1,6-linked ester was straightforward as outlined in Scheme 6. We were able to convert alcohol 23 to aldehyde 24 using Swern oxidation conditions. Wittig reaction was followed by olefin reduction and saponification to bring the sequence as far as 26. Esterification of 26 with olefin alcohol la, mediated by DCC, then afforded the target ester 27 in good overall yield (13). 

Esters. Most acryhc acid is used in the form of its methyl, ethyl, and butyl esters. Specialty monomeric esters with a hydroxyl, amino, or other functional group are used to provide adhesion, latent cross-linking capabihty, or different solubihty characteristics. The principal routes to esters are direct esterification with alcohols in the presence of a strong acid catalyst such as sulfuric acid, a soluble sulfonic acid, or sulfonic acid resins addition to alkylene oxides to give hydroxyalkyl acryhc esters and addition to the double bond of olefins in the presence of strong acid catalyst (19,20) to give ethyl or secondary alkyl acrylates. 

Next step of this synthesis consisted in the conversion of alcohol (17) to pisiferic acid (1) and this has been described in Fig. (3). The alcohol (17) in hexane was treated with Pb(OAc)4 in presence of iodine at room temperature to obtain the epoxy triene (19) (51%) whose structure was confirmed by spectroscopy. Treatment of (19) with acetyl p-toluene-sulfonic in dichloromethane yielded an olefinic acetate (20) and this was hydrogenated to obtain (21). The compound (22) could be isolated from (21) on subjection to reduction, oxidation and esterification respectively. The conversion of (22) to (23) was accomplished in three steps (reduction with sodium borohydride, immediate dehydration in dichloromethane and catalytic hydrogenation). Demethylation of (23) with anhydrous aluminium bromide and ethanethiol at room temperature produced pisiferic acid (1). Similar treatment of (23) with aluminium chloride and ethanethiol in dichloromethane yielded methylpisiferate (3). 

These represent hydrolysis of diethyl ether, synthesis of iV-mono-ethylaniline from alcohol and aniline, and dehydration of alcohols to olefins. Promoting the catalyst differently effects these reactions, in accord with the multiplet theory. Thus, the addition of the oxides of Fe, Ni, and Zn accelerates the first reaction and slows down the second and the third one 351). Incidentally, as has been found by the author and Sokolova 352), Nb20s and TaEOs are good catalysts in obtaining monoethylamine as well as in esterification of alcohols with acids, and they carry out the condensation of acetaldeyde into crotonaldehyde 353). 

This afforded primary alcohol 18, which was oxidized to the aldehyde and the latter subjected to Z-selective StiU-Gennari olefination to a,P-enoate 19. Treatment of 19 under acidic conditions caused complete desilylation and lactonization, giving dihydropyrone 20. Debenzylation and protection of the vicinal diol moiety gave acetonide 21, which was converted into (+)-phomopsolide B by means of esterification with tiglic add followed by acetal deavage [8g]. In this synthesis, the two stereocenters of the starting diethyl n-tartrate become carbon atoms C-5/C-6 of the final dihydropyrone ring. 

As part of a medicinal chemistry program [16] directed toward discovering new muscarinic receptor ligands, a series of endo- and exo-2-alkyl-2-aza-bicyclo[2.2.1]heptan-5-ol (38 and 39) and endo- and exo-2-alkyl-2-aza-bicyclo[2.2.1]heptan-6-ol (40 and 41) esters have been synthesized from 2-alkyl-2-azabicyclo[2.2.1]heptan-5-enes (Scheme 2.4). Oxidation of the olefin and stereochemical manipulation of the secondary alcohols followed by esterification of the azanorbornene products provided the different isomers required for systematic investigation of the structure-activity relationships of this structural series. 

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