Organometallic compounds with epoxides

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

Regioselectivity of C—C double bond formation can also be achieved in the reductiv or oxidative elimination of two functional groups from adjacent carbon atoms. Well estab llshed methods in synthesis include the reductive cleavage of cyclic thionocarbonates derivec from glycols (E.J. Corey, 1968 C W. Hartmann, 1972), the reduction of epoxides with Zn/Nal or of dihalides with metals, organometallic compounds, or Nal/acetone (seep.lS6f), and the oxidative decarboxylation of 1,2-dicarboxylic acids (C.A. Grob, 1958 S. Masamune, 1966 R.A. Sheldon, 1972) or their r-butyl peresters (E.N. Cain, 1969). 

Reactions of the epoxide of 1-butene with CH3Li gives a 90% yield of 3-pentanol. In contrast, reaction with CH3MgBr under similar conditions gives an array of products, as indicated below. What is the basis for the difference in reactivity of these two organometallic compounds toward this epoxide ... 

Ethyl 2,3-epoxypropanoate is a very interesting chiron. It may be opened by various organometallic compounds such as dialkyl, diaryl, and divinyl lithium cuprates, dialkylmagnesium cuprates, trialkylalanes and aluminum acetylides.5 6 The epoxide ring is attacked regiospecifically at the p-position and produces a-hydroxy esters exclusively without racemization. The same result is observed with... 

The isocoumarin and the dihydroisocoumarin ring systems occur widely in nature Their synthesis by lithiation method is according to type C and involves ortho metalation of N-methyl arylcarboxamides. The organometallic compounds on treatment with electrophilic reagents such as an epoxide or allylbromide followed by hydrolysis and cyclisation furnish the dihydroisocoumarins. Bromination at benzylic position followed by dehydrobromination then gives the isocoumarins themselves. 

---