Search

Chemical research has discovered that an arylketone moiety with Cp2Ti(PMe3)2 or CP2Ti(CO)2 will act as catalyst in the production of gamma-butyrolactones from enones. Research is continuing to increase knowledge on the mechanics and kinetics of the chemical reaction. Further catalysis experiments using nonaryl ketone-containing substrates with electron transfer catalysts will be performed.

A new process that uses bis(trimethylphosphine)titanocene as a catalyst in the reductive cyclization of enones to cyclopentanols is introduced. The catalyst, which is sensitive to both air and moisture, is regenerated by the cleavage of the titanium-oxygen bond in a metallacyclic intermediate by a silane. Besides regenerating the catalyst, the reaction affords a titanocene alkyl hydride that, in turn, reduces to a silyl-protected cyclopentanol. Subsequent hydrolysis affords the end product.

The use of Cp2Ti(CO)2 as the first early metal-based catalyst for the cycloisomerization of enynes and dienynes to 1,4-dienees and 1,4,5-trienes is described. The results showed that the titanocene system offered complementary reactivity and selectivity similar to late-transition-metal-catalyzed processes. The optimum conditions and mechanisms for the cycloisomerization reactions are described.

The first early transition metal-catalyzed carbonylation of enynes, which uses Cp2Ti(CO)2(super 6) and CO to produce cyclopentenones, is reported. The Cp2Ti(CO)2 system demonstrates a new reactivity mode for an early transition metal carbonyl as well as manifests an unexpectedly higher level of functional group compatibility compared with other group 4 metallocene cyclizations and puzzling mechanistic differences from the related iminocyclopentene synthesis. Moreover, it displays a higher tolerance for substituted alkenes than related cobalt procedures.

A diastereoselective and high-yielding synthesis of gamma-butyrolactones is described. The scheme uses enones as starting material and is either by Cp2Ti(PMe3)2 or uses Cp2Ti(PMe3)2 as a pre-catalyst. The formation of a fused butenolide from an ynone utilizing the same metal reagent is also described. The optimum conditions and mechanisms for the reactions are presented.

The reductive cyclization of an alkene or an alkyne with a heteroatom containing functional group is now possible with the help of an early transition metal catalysts like titanium. Early transformtion metal catalysts are often incompatible with polar functional groups, but in this type of transformation, enones containing allylic ethers or esters are tolerated. Efforts towards the development of more synthetically useful methods including those that afford more functionalized and/or enantiomerically enriched products are in progress.

Research was conducted to examine a Pauson-Khand type conversion of enynes to bicyclic cyclopentenones by means of precatalyst titanocene dicarbonyl. The approach displayed extraordinary functional group tolerance for a group 4 metallocene-catalyzed process. The synthetic scope of the Ti catalyst system seems to be complementary to Co-based protocols with respect to alkyne substitution and similar to the Ru- and Rh-based catalysts.