Search

Palladium(O)-catalyzed cyclodimerization and cycloisomerizations of enyne esters is described. Uncommon six-membered ring products were predominantly formed with concomitant enyne metathesis products when enyne esters bearing a methallyl moiety were used.

Research has been conducted on the monomeric titanocene(III) complex Cp (sub)2 TiPh. The use of this complex in investigating the catalyzed inter- and intramolecular pinacol couplings is discussed.

The rapid synthesis of P-chiral amino acid-derived phosphonamidic anhydrides is demonstrated. The subsequent ring-closing metathesis (RCM) reaction to yield amino acid-derived bicyclic phosphonamidic anhydrides derived from the vinylphosphonamidic anhydrides is also described.

A single-electron transfer from trivalent phosphorus compounds to the photoexcited state of rhodamine 6G (Rho+*) to quench the fluorescence from Rho +* is investigated. The irreversibility results from high reactivity of radical cation Z3.+ as an electrophile toward a nucleophile.

A Ti(III)-mediated reductive coupling of cyanoketones and ketoesters leading to alpha-hydroxycycloalkanones has been developed. The process involves the coordination of the Ti(III) complex, Cp2TiPh, to a cyano group or an ester carbonyl group for the efficient cyclization of the induced-titanium(IV)-substituted ketyl radical to the Ti(III)-coordinated polar multiple bonds. The Cp2TiPh-mediated reductive radical cyclization of cyanoketones in both the 5- and 6-exo modes successfully provided an easy entry to the 5- and 6-membered alpha-hydroxycycloalkanones.

N-allyltrichloroacetamides containing various substituents attached to the nitrogen atom undergo copper chloride- and bipyridine catalyzed cyclization reaction to produce high yields of beta,gamma trichlorinated gamma-lactams. The reaction does not exhibit temperature dependence from -78 degrees Centigrade to room temperature. The cyclization reaction has good selectivity with the cis and trans ratio of the final product exhibiting dependence on the substituent.

The synthesis of three 4-substituted bis(oxazolinyl)pyridines and their rhodium complexes allows the study of the effect of their substituents in the catalytic asymmetric hydrosilylation of ketones. The study shows that introduction of substituents affects the critical reaction temperature at which the rhodium catalyst and silane effect smooth reduction of the ketone. Electron-withdrawing groups speed up the reaction while electron-donating groups slow it down. The substituents also enhance the enantioselectivity up to 90-94%.

The (3.3)-sigmatropic rearrangement of allyl trichloroacetimidates followed by ring closure of the acetamides provides the key steps in the novel diastereoselective synthesis of trichlorinated gamma-lactams from allylic alcohols. The process results in 60-80% yields without producing the corresponding delta-lactams. The reaction mechanism involves four envelope- shaped transition states. The first state prefers exo cyclization, the second prefers endo cyclization, the third leads to formation of a cis-fused bicyclic system, while the fourth is highly trans-selective.

Polybromoanisoles and aliphatic Grignard reagents can undergo metal-halogen exchange reaction forminghalide aromatic Grignard reagents and cyclopenta(b)benzofuran skeletons. The reaction between polybromoanisole and alkyl Grignard reagents in the presence of tetrahydrofuran exhibits the exchange of only one bromine atom that is orthoto the methoxy group. The reaction opens a new route for the study of selectiveorganic functional group conversion.

Two silylmethylated fullerenes, HC(60)CH2SiMe2Y formed in THF and (Me2YSiCH2)2C(60) produced in toluene, were generated during the addition reactions of Me2SiYCH2MgCl to C(60). Chemical modification of the organosilyl group facilitates the production of fullerene derivatives from these silylmethylated fullerenes.

A convenient and highly stereoselective method for the synthesis of a diversity of [alpha]-1-C-substituted-1,4-dideoxy-1,4-imino-D-galactitol, which constitute novel original galactofuranoside mimicks is reported. The new 1,4-imino-D-galactitol derivatives obtained is found to be inhibitors of (UDP-galactopyranose mutase) (UGM) from Escherichia coli and exhibited activities toward galactopyranose enzyme.

A study was conducted to analyze the formation of exo-methyl-enecyclopentanes from alpha,omega-dienes under ruthenium catalysis. Cycloisomerization was catalyzed by RuCl3 3H2O and (Ru(cod)Cl2)n. A novel and versatile protocol for synthesizing functionalized cyclopentanes and an associated nitrogen heterocycle were developed. The protocol supported a number of benefits compared against other techniques.

A unique Cp*Ru(cod)Cl-catalyzed cycloaddition of 1,6-heptadiynes with allylic ethers is shown as an electronically nonactivated alkyne-alkene coupling. The process is a practical method for the synthesis of functionalized bicyclic cyclohexadienes. Its primary benefit is that it does not employ environmentally degrading solvents such as halogenated alkanes or benzene derivatives. Allylic ethers are employed as a solvent and are easily recovered by simple distillation.

The electrical properties of C(sub 60) is severely changed by the introduction of functional groups. The silyl triflates act as reagents in the reaction of C(sub 60) with different alcohols and phenols by the Si-O bonds. New C(sub 60) derivatives are produced with the silylation of OH groups to this reagents. Organosilone chlorides and triflates are also used in the organic synthesis with different kind of nucleophiles. A wide variety of fullerene compounds are prepared from the C(sub 60).

In the presence of a catalytic amount of a rhodium(I) complex, allenenes undergo cycloisomerization reactions resulting in the selective formation of exo-alkylidenecarbocycles and heterocycles. In the catalytic system of rhodium complexes with triaryl phosphites, cyclic 1,4- or 1,5-dienes are formed in good to excellent yields in the formal exo-cyclization mode via the metallacycle intermediate having an exo-alkylidene moiety. In this cycloisomerization, (E)- and (Z)-allenenes are transformed stereospecifically to the corresponding cyclic (E)- and (Z)-1,4-dienes, respectively. On the other hand, the reactions under carbon monoxide atmosphere exclusively afford seven-membered-ring products through an endo-mode cyclization. The unusual cyclization involves an allylic C-H activation process. The allenene bearing a silicon substituent at the olefinic terminus incorporates carbon monoxide to give the corresponding [2+2+1] cycloaddition product. This result apparently indicates that the catalysis of the rhodium complex is explained in terms of the oxidative cyclization of an allenene to furnish the key exo-alkylidene metallacycle intermediate at the first stage of the catalysis. [ABSTRACT FROM AUTHOR]