ABSTRACT
Conjugate addition of heteroatom nucleophiles to carbon-carbon double bonds conjugated with a strong electron-withdrawing group is one of the most important new bond-forming strategies in synthetic organic chemistry. Among the methods for these Michael additions, Lewis acids have shown the best promoter activity, and in particular, the use of reagents impregnated over inorganic supports is rapidly increased. With the increase of environmental consciousness in chemical research, the solvent-free Michael addition has attracted our attention. In continuation of our ongoing program to develop synthetic protocols utilizing cerium trichloride, we report an extension of the CeCl(3).7H(2)O/NaI combination supported under solvent-free conditions to promote heteroatom Michael addition. Using neutral alumina (Al(2)O(3)) as solid support permits us to circumvent some of the problems associated with the procedure where the inorganic support is silica gel. The CeCl(3).7H(2)O/NaI/Al(2)O(3) system works well for hetero-Michael additions utilizing weakly nucleophiles such as imidazoles and carbamates, and also the reaction proceeds with good yields in the case of Michael acceptors different from alpha,beta-unsaturated carbonyl compounds. An important synthetic application of this our methodology is the intramolecular aza-Michael reaction in producing 4-piperidinone derivatives, which are of interest as synthetic intermediates toward important classes of heterocycles.
ABSTRACT
Alkylation of indoles by means of the Michael addition has been the subject of a number of investigation. It is well established that regioselectivity in the additions of indoles to electron-deficient alkenes is strongly controlled by the reaction medium. In a continuation of the work on developing greener and cleaner technologies, the cerium(III) chloride heptahydrate and sodium iodide combination supported on silica gel catalyzes the alkylation of various indoles with alpha,beta-unsaturated ketones giving 3-(3-oxoalkyl)indole derivatives in good yields. The substitution on the indole nucleus occurred exclusively at the 3-position, and N-alkylation products have not been observed.
ABSTRACT
Readily preparable morpholine amides hitch in good yields with organocerium reagents to produce ketones. Even in the presence of substrates and reagents with high steric hindrance, the organometallic compounds prepared from dry cerium(III) chloride and organomagnesium or organolithium compounds at -78 degrees C add cleanly to morpholine amides. The low cost of starting materials makes this new scheme of synthesis very interesting for the preparation of biologically important pheromones.
