Enolate anions, alkylidene

Finally, the coupling reaction of vinyl and alkylidene (see Alkylidene) ligands in complexes of the type (166) results in the formation of (jj -allyl)FeCp(CO) complexes (equation 38). The vinyl substituent in these reactions is most often an enolate, whereas the alkyhdene unit is formally of the Fischer carbene type. The ultimate product depends upon the starting material and additional reagents. In the case of (ferra-/3-diketonato)difluoroboron complexes (167), the resulting anion is isolated as tetramethylammonium salt (168). In the case of Fp(acyl) complexes as starting materials, benzoylation of the resultant anions gives complexes (163 ... 

Ethoxy-5,6-dihydro-4//-l,3-oxazines (111) react with enolates and related compounds at C-2 ethanol is lost and the corresponding 2-substituted dihydro-1,3-oxazine is formed. Depending upon the nature of the substituent endo-exo double bond, tautomerism can be observed. Thus, a reaction with the anion of malononitrile yields the 2-alkylidene-3,4,5,6-tetrahydro-l,3-oxazine (112) rather than the 2-alkyl-5,6-dihydro-1,3-oxazine (113) (Scheme 27) <86JHC701>. 

The last step of an efficient protocol for the one-pot synthesis of biologically important (Z)-y-substituted-a, P-didehydroglutamates 21 starting from A-alkylidene-glycinates 19, involves the C-alkylation of intermediate alkaline dienolates 20 in THE. However, capture of 20 with an excess of electrophiles, such as Mel, failed even in the presence of DMPU as an anion activator. The generation of "naked enolates by using 18C6 allowed for a smooth and efficient reaction (Eq. 19). 

The masked acrylate anion (70) can be condensed with epoxides leading to a-alkylidene-lactones (71) after a retro-Diels-Alder reaction the generality of this method remains to be seen. Compounds (71) can also be obtained in generally moderate overall yields from enolates of y-trimethylsiloxy-nitriles by... 

---