Metal catalyzed carbonylation of aziridines, alkynyl epoxides and alpha-allenic alcohols.
|Title:||Metal catalyzed carbonylation of aziridines, alkynyl epoxides and alpha-allenic alcohols.|
|Authors:||Piotti, Marcelo Eduardo.|
|Abstract:||This thesis describes the results obtained in the metal catalyzed carbonylation of aziridines, alkynyl oxiranes and $\alpha$-allenic alcohols. Aziridines undergo carbonylation and ring expansion when they are treated with catalytic amounts of Co$\sb2$(CO)$\sb8$ under 33 atm of carbon monoxide in ether solvents at 100$\sp\circ$C, to afford $\beta$-lactams in good to excellent yields. This reaction is applicable to aziridines containing alkyl or aryl groups at the ring carbons, and alkyl, aryl or acyl groups at the nitrogen atom. The reactions in most cases are regioselective, with carbon monoxide insertion occurring into the less substituted ring carbon-nitrogen bond. The carbonylation reaction is also stereoselective, giving trans-3,4-disubstituted $\beta$-lactams when cis-2,3-disubstituted aziridines are used, and vice versa. This stereoselectivity was maintained when fused bicyclic aziridines were subjected to carbonylation, affording the previously unknown trans-7-azabicyclo (4.2.0) otan-8-one derivatives. An X-ray study of one of these novel compounds reveals that the four membered ring contains structural features similar to those found in biologically active $\beta$-lactams, suggesting that these compounds might have considerable acylation power. The mechanism of the reaction involves nucleophilic ring opening of the aziridine ring by the in situ generated Co(CO)$\sb4\sp-$ anion. The carbonylation of aziridines is described in Chapter 2. Palladium (0) complexes catalyze the carbonylation of alkynyl oxiranes to 5-hydroxy-2,3-dienoates in the presence of 20 atm of carbon monoxide and methanol as the solvent. The reaction takes place under mild conditions (room temperature, one to two hours for complete conversion.) The mechanism involves the formation of a zwitterionic $\sigma$-allenylpalladium complex. When the carbonylation reaction is effected on alkynyl oxiranemethanol derivatives, partially saturated furan-3-ol compounds are obtained. These compounds are presumably formed by spontaneous cyclization of a nonisolable allenediol intermediate. Hydrofuran derivatives containing an exo or endo double bond are obtained depending on the substitution pattern of the initial epoxide. An interesting application of this reaction is the synthesis of a chiral furan-3-ol by carbonylation of a chiral epoxy alcohol obtained by Sharpless epoxidation. These results are described in Chapter 3. Chapter 4 describes the carbonylation of $\alpha$-allenic alcohols to $\alpha$-vinylacrylic acids catalyzed by a novel cationic aquo hydride palladium complex. The reaction requires the presence of catalytic amounts of p-toluenesulphonic acid and 20 atm of carbon monoxide to take place. This complex generates a palladium (0) species in situ, which is the active catalyst. The formation of a $\pi$-allylpalladium complex would be a key step in this reaction.|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|