Trigonal prochiral centers

Trigonal carbon atoms 680, 681 Trigonal prochiral centers 480,481 Triiodothyronine 572 Trimethoprim 805s... 

A prochiral center is a trigonal carbon of C=0 and C=C that is not a stereogenic center but can be made chiral by addition reactions. 

The reduction of cyclic 2,2-disubstituted 1,3-diketones 136 (Fig. 38) can be regarded as an example of an enzyme-catalyzed distinction of a substrate containing two trigonal carbonyl centers with stereotopic faces and one prochiral tetrahedral carbon center where monoreduction generates two chiral centers. All of the products 137 and 138 were obtained with high e.e. [173-185]. Cyclohexanoid 1,3-diketones have been reduced with low dia-stereoselectivity as compared to the cyclopentanoid series [173,184,186-196]. Dimeriza tion under participation of acetaldehyde produced by fermenting yeast has occasionally... 

The concept of prochirality can also be applied to trigonal centers, i.e., to faces of suitable molecules. In acetaldehyde (LXI), the two faces of the molecule are not... 

Most often, asymmetry is created on conversion of a prochiral trigonal carbon of carbonyl, enol, imine, enamine, and olefin groups to a tetrahedral center. One of the easiest methods for the preparation of optically active alcohols is the reduction of prochiral ketones. This transformation is achieved using chiral reductants in which chiral organic moieties are ligated to boron or to a metal hydride (Table 4.9). 

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