Zinc, organo- reagents aldehydes

There are many examples of asymmetric addition of organo-metallic reagents to aldehydes (chapter 27) and the one that works here uses Seebach s TADDOL 51 as a ligand for zinc.8 The TAD-DOL 51 is prepared from tartaric acid and used as its titanium (IV) complex to catalyse the addition of the organozinc compound to acrolein. After photochemical cyclisation in the presence of Cu(I), the bicyclic alcohol 53 was isolated in good yield and >98% ee. 

In 1887, the Russian chemist Sergei Reformatsky at the University of Kiev discovered that treatment of an a-haloester with zinc metal in the presence of an aldehyde or a ketone followed by hydrolysis in aqueous acid results in formation of a /3-hydroxyester. This reaction is similar to a Grignard reaction in that a key intermediate is an organo-metallic compound, in this case, a zinc salt of an ester enolate anion. Grignard reagents, however, are so reactive that they undergo self-condensation with the ester. 

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