Search

Titanated pyridines in highly selective manner were produced directly by the four-component process that involves two acetylenes, a nitrile, and a divalent titanium alkoxide reagent, Ti(O-i-Pr)(sub 4)/2i-PrMgCl. Synthetic application of this process is illustrated in the preparation of optically active pyridines and medically useful compounds.

Results describe the generation of the silylethylene-titanium alkoxide complex, its ability to form carbon-carbon bonds, and its functionalization with unsaturated compounds.

This paper discusses the organic synthetic reactions in which olefins with a carbon-carbon unsaturated bond reacts with titanium both at carbanion or transition metal characteristic reactions at tandem. Such reactions lead to the generation of alkene- or alkyne-titanium complexes eventually giving rise to organotitanium complexes.

A study on group 4 metallabicycles used in organic synthesis reports the scope of two essential reactions of a generation of new alkoxy-ligand-containing titanabicycles for carbon-carbon bond formation. These two reactions are aldehyde addition and allylation. Results of the study suggest that the bicyclization of enynes and diynes mediated by low-valent titanium complex and the subsequent selective addition to aldehydes feature new applications which are complementary to those of similar matallacycles of other group 4 transition metals.

It is possible to produce 1-alkenyl-2-alkylidenecyclopentanes in moderate to good quantities after aqueous workup by treating a range of 1,2-dien-7-ynes with a slight excess of (eta-2-propene)Ti(O-i-Pr)2, prepared in situ from Ti(O-i-Pr)4 and 2 equivalent of i-PrMgCl in ether. This approach made it possible to investigate whether a chiral allenyne treated with (eta-2-propene)Ti(O-i-Pr)2 will produce optically active titanabicycles. Cyclization followed by the selective reaction of the resultant titanbicycle with an electrophile is a valuable entry to the metal-promoted intramolecular cyclizations of bis-unsaturated compounds.

Low-valent titanium-mediated cyclization of bis-unsaturated compounds with a conjugated ester moiety is a versatile method for producing mono- and bicyclic compounds. Diastereoselective reaction of carbonyl compounds allows extending side chains from the cyclization product, stereoselective cyclization allows constructing the ring structure of the defined stereochemistry and these transformations enable regioselective aldol formation from a symmetrical ketone. These advantages make this method very viable for preparing stereogenic centers with a cyclic structure.

ZnI2, LiH and Cp2TiCl2 in a ratio of 1:2.2:0.1 catalyze the hydrozincation of butadienes and 2-alkylbutadienes yielding allyl zinc reagents in THF. The zinc species react with different compounds involving aldehydes or CO2, producing a single homoallyl alcohol or a single carboxylic acid of the four possible regioisomers. Formation of a single product reveals the regioselectivity associated with the formation of allylzinc and carbonyl addition.

2-Aryl-3-(sulfonyl)-5,6-dihydro-2H-pyran is produced when arylmethyl 4-(sulfonyl)-3-butynyl ether and a catalytic amount of [Rh.sub.2][(tfs).sub.4] (tfa = C[F.sub.3]C[O.sub.2.sup.-]) are heated. 2-(5-Sulfonyl-4-pentynyl)tetrahydrofuran lacking a benzyl substituent has produced a different product, 9-sulfonyl-1-hydroxy-8-nonen-4-one, upon reaction with the same rhodium catalyst at reflux in wet toluene.

An yttrium reagent has reacted with a metalated alkene such as a vinyl Gringnard reagent, which has led to the new method of producing 1,2-dimetalated ethane. This reagent has new characteristics that are complementary to those of the existing 1,2-dimetalated ethanes, which are already used in organic synthesis.

The simple method to synthesize 1,4-diaza(or partially oxa)-2-cycloalkenes based on a new copper-catalyzed double amination of haloacetylene is reported. The procedure can be applied to obtain unsaturated heterocyclic compounds having two heteroatoms.

A Grignard addition to olefins uses the radical species generated by the aerial oxidation of Grignard reagents, and enables a one-pot, three-component coupling process of a Grignard reagent, olefin and oxygen in air, to directly yield alcohol. The reaction provides a very simple process free of additional or toxic reagents and no transition metal salts or organotin.

The functionalized conjugated diene-titanium alkoxide complexes provide versatile templates for organic synthesis, where the functional group promotes the complex formation, controls regio- and stereoselectivities of the subsequent reactions, and imparts a chiral element to the template.

A titanium alkoxide-based intramolecular cyclization of enol ester and acetylene is described. Further investigation on the utility of tandem cyclization as well as the application of its products is in progress.

A novel transformation based on the metalative Reppe reaction of acetylenes and a titanium(II) reagent, which directly and regioselectively produces benzyltitanium compounds is reported. Further, a novel preparation of benzyltitanium compounds, which may have a functional group such as ester or amide, from three acetylenes and the titanium alkoxide, is described.

Results demonstrate that a one pot selective synthesis of pyridines and metalated pyridines proceeds with a combination of two acetylenes, various nitriles, and the titanium alkoxide reagent. Data indicate that starting with alkynamide or alkynoate, the reacion facilitates regioselective three-component coupling process.

The unidirectional isomerization of titanted vinylallenes to cyclobutenyltitanium compounds is investigated.

The organized assembly of acetylene molecules on titanium resulted in a new form of acetylene cyclotrimerization.

A regio and stereoselective addition reaction of aldehydes, ketones or imines to carbon-titanium bonds is reported.

A method to generate a regioisomer through hydrometalation via a new route is presented. The new route consists of the formation of the acetylene-metal complex and then a regioselective monoprotonation. The method was found to be effective when used on several silylalkynes, including the (Beta-silylalky)titanium reagent. The resulting alkenyltitanium species were confirmed by iodinolysis or deuteriolysis. Results also indicated that the method can be extended to a conjugated enyne system.

The selective reactions of aldehydes with bicyclic titanacylopentadienes or titanacyclopentenes formulated in situ from inexpensive Ti(O-i-Pr)2, i-PrMgCl, 1,6- or 1,7-diynes or enynes, and (eta2-propene)Ti(O-i-Pr)2 are shown. Alipathic aldehydes facilitated the production of the chemicals in substantial quantities under standard reaction conditions. However, for an aromatic aldehyde, the application of TiCl-(O-i-Pr)3 instead of TiCl2(O-i-Pr)2 is suggested as the additive.

A novel type of cyclizations of acyclic precursors for the preparation of bicyclic systems, consisting of two different kinds of cyclizations in tandem, starting from the title unsaturated compounds, is presented. The initial step is based on the titanium-mediated cyclization of dienes and enynes, followed by the second ring closure through the addition of the resulting carbon-titanium bond to an electron-deficient moiety in the same molecule with accompanying incorporation of an electrophile. Substrates determine the patterns of reactions, with type I occurring with alpha,beta-olefinic esters and type II involving the reactions of alpha,beta-acetylenic esters.

The enhanced reactivity of alpha,beta-unsaturated ester and amide towards radical addition comes because of the presence of Lewis acid. The effect of LA (Lewis acid) was experimented in butyl radical addition to alpha,beta-unsaturated ester and amide. The chemoselectivity of the substrate changed due to the complexation of LA to the substrate. The alpha, beta-unsaturated ester is a more reactive accepter than the corresponding amide, because the former has more electron deficient enone moiety.

A stereoselective hydrozincation enables the direct synthesis of alkenylzinc reagents, which find application as carbon nucleophiles. This reaction involves a combination of ZnI2 and LiH in the ratio 1:2 in THF in the presence of a titanium catalyst and results in 99% yield of the product. Stirring the reaction mixture at rt for 24 h results in the alkenylzinc reagent. However, terminal acetylenes cannot be subject to hydrozincation.

The reaction of iodobenzene with an enyne catalyzed by Pd(0) was performed to test the feasibility of alkylative cycloaddition to obtain substituted bis(alkylidene)cycloalkanes which exhibit stereospecific properties. The process gave the desired alkylated cycloadduct which established the stereochemistry between one of the vinyl protons and the aromatic ring protons. The stereochemistry of the products from reactions with beta-bromostyrene were also assigned.