Magnesium in methanol reduction and reaction of its intermediates involved

Abstract

I. Magnesium in methanol reduction of aliphatic and aromatic $\alpha,\beta$-unsaturated esters afforded the corresponding saturated esters in high yields. This reduction method was also applicable for the reduction of azlactone derivatives. Of special interest was the reduction of indole-2-carboxylate and carboxamide to the corresponding indoline derivatives. This method was found to be selective for the conjugate reduction of various $\alpha$-oxoketene dithioacetals. During the reduction study, efficient air oxidizing method for the regeneration of indole-2-carboxylate or amide from the corresponding indoline derivative was developed. (S)-N-methyl-2-hydroxy methyl indoline prepared from (S)-indoline-2-carboxylic acid was used as chiral auxiliary for the asymmetric reduction of acetophenone. Optical purity of phenyl ethanol was achieved up to 42\% ee. Various conjugated ketene dithioacetals derived from $\beta$-keto esters were found to be a potent synthetic intermediate. Magnesium in methanol reduction of ketene dithioacetals afforded potent synthetically useful $\alpha$-dithiolanyl substituted $\beta$-keto esters. Highly functionalized synthetically useful $\alpha$-pyrone were prepared from ethyl (1,3-dithiolan-2-ylidene) acetoacetate derivatives. Thus easy preparation of these ketene dithioacetals, $\alpha$-dithiolanyl substituted $\beta$-keto esters, $\alpha$-pyrone, 1,3-butadiene, 2-(1,3-dithiolanyl) acetone, and $\alpha$-(1,3-dithiolanyl)-crotonate have been demonstrated. II. Gossypol tetramethyl ether was prepared in 60\% yield by the modification of the known method. Isomeric gossypol tetramethyl ether dilactol form was obtained in 95\% yield by hydrolysis of gossypol hexamethyl ether with aqueous acetic acid and this isomeric gossypol tetramethyl ether could be brought back to its original gossypol hexamethyl ether dilactol form by methanolysis. Gossypol nitrile tetramethyl ether was isolated during the hydrolysis of gossypol anhydro oxime derivative. ...