Esters hydrochlorination

The reaction of 3-cyclohexene-1-carboxylic acid with ECH (molar ratio 1 8) was investigated at 65-85 °C in presence of a catalyst (KCl or tetramethylammo-nium chloride). After 2 h the formation of the chlorohydrin ester was completed with 100% quantitative yield. However, the hydrochlorination results in a low yield of epoxy groups and a low conversion of chlorohydrin to epoxy groups. The alkali partial consumption for hydrolysis of the ester groups, even at room temperature, is another reason. 

Table III shows the results of hydro-bromination and hydrochlorination of the ethyl trans-cinnamate inclusion complexes. No hydrochlorination was observed at various temperatures after long exposure of hydrogen chloride gas similar to the reaction of trans-cinnamic acid [14]. Addition of hydrogen bromide to the ester gave an optically active and regioselective product, ethyl R-(+)-3-bromo-3-phenyl-propanoate in 46 % e.e. from the a-cyclodextrin, or ethyl S-(-)-3-bromo-3-phenylpropanoate in 31 % e.e. from the 3-cyclodextrin inclusion complex.

In addition to the methods described above, prenol (51) can be prepared from methyl-butynol (43) by rearrangement to prenal (52) using a titanium alkoxide/copper chloride catalyst [69, 70] followed by selective hydrogenation using a ruthenium rhodium tris( 7-sulfonatoyl)phosphine trisodium salt (TPPTS) catalyst [71, 72]. However, it is more usual to prepare the prenyl esters by nucleophilic substitution of a carboxylate anion on prenyl chloride [503-60-6] (56) which, in turn, is available through hydrochlorination of isoprene [78-79-5] (1). This hydrochlorination often employs copper ions as catalysts. These processes are shown in Fig. 8.14. 

Fabio Doctorovich of the Universidad de Buenos Aires reported (/. Org. Chem. 2008, 73, 5379) that hydroxylamme in the presence of an Fe catalyst reduced alkenes such as 1, but not ketones or esters. Erick Carreira of ETH Zurich developed (Angew. Chem. Int. Ed. 2008, 47, 5758) mild conditions for the hydrochlorination of mono-, di- and trisubstituted alkenes. Ramgopal Bhattacharyya of ladavpur University established Tetrahedron Lett. 2008, 49, 6205) a simple Mo-catalyzed protocol for alkene epoxidation. 

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