Titanocene(II)-promoted, one-pot, three-component coupling of thioacetals, alkynyl sulfones, and carbonyl compounds: highly stereoselective formation of tert-homopropargyl alcohols

Photoinduced synthesis of alkylalkynyl sulfones through a reaction of potassium alkyltrifluoroborates, sulfur dioxide, and alkynyl bromides

A photoinduced reaction of potassium alkyltrifluoroborates, sodium metabisulfite, and alkynyl bromides under visible light irradiation at room temperature is developed.

N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism

The remarkable activation of stable titanocene dichloride (Cp₂TiCl₂) was achieved using N-donor ligand urea in an alcoholic solvent, leading to the formation of a Ti(iv) species [(MeO)₂Ti(NHCONH₂)]⁺, the existence of which was verified by ESI-MS, ESI-MS/MS, and NMR. Catalyzed by the newly formed Ti(iv) species, a myriad of 3,4-dihydropyrimidin-2-(1H)-ones were produced via a three-component Biginelli reaction. Further mechanistic investigation indicated that the Biginelli reaction had taken place via the imine route.

Stable titanocene dichloride (Cp₂TiCl₂) was activated by the N-donor ligand urea to form [(MeO)₂Ti(NHCONH₂)]⁺, which catalyzed the Biginelli reaction to produce 3,4-dihydropyrimidin-2-(1H)-ones.

Recent advances in the sulfonylation of C–H bonds with the insertion of sulfur dioxide

Recent advances in the sulfonylation of C–H bonds with the insertion of sulfur dioxide are summarized. C–H bond sulfonylation under transition metal catalysis or through a radical process has been developed. In some cases, the sulfonylation can be performed under catalyst- and additive-free conditions, or can be facilitated by visible light irradiation. The efficiency is also studied by merging the radical process and metal catalysis.

Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Aryl Tosylates

Decarboxylative coupling reactions of alkynyl carboxylic acids with aryl tosylates were developed in the presence of a palladium catalyst. Among the commercially available phosphine ligands, only 1-dicyclohexylphosphino-2-(di-tert-butylphosphino-ethyl)ferrocene (CyPF-tBu) showed good reactivity. The reaction took place smoothly and gave the decarboxylative coupled products in moderate to good yields. This demonstrates the excellent functional group tolerance toward alkyl, alkoxy, fluoro, thiophenyl, ester, and ketone groups. In addition, alkyl-substituted propiolic acids, such as octynoic and hexynoic acids, were coupled with phenyl tosylate to provide the desired products. We found that the electronic properties of the substituents on the phenyl ring in arylpropiolic acids are an important factor. The order of reactivity was found to be aryl iodide > aryl bromide > aryl tosylate > aryl chloride. However, aryl chloride-bearing electron-withdrawing groups showed higher reactivity than those bearing aryl tosylates.

Solvent strategy for unleashing the Lewis acidity of titanocene dichloride for rapid Mannich reactions

The remarkable activation effect of alcohol solvent on kinetically inert titanocene dichloride was found to promote rapid three-component Mannich reactions.

Preparation of syn-tertiary homoallylic alcohols utilizing allenyltitanocenes generated by reductive titanation of gamma-trimethylsilylpropargylic carbonates

syn-Tertiary homoallylic alcohols were obtained by the reaction of alpha-silylallenyltitanocenes generated by the reductive titanation of gamma-silylpropargylic carbonates with Cp(2)Ti[P(OEt)(3)](2) with ketones and following desilylation and partial hydrogenation. High diastereoselectivity was observed when aromatic and alpha,beta-unsaturated ketones were employed.

Regio- and stereoselective formation of conjugated dienes by titanocene(ii)-promoted alkylation of propargyl carbonates

Conjugated dienes were produced with complete regio- and stereoselectivity by the titanocene(ii)-promoted alkylation of propargyl carbonates via the formation of 2,3,4-trisubstituted titanacyclobutenes.

Highly diastereoselective addition of allyltitanocenes to ketones

A route with less congestion: A practical method for the highly diastereoselective preparation of anti tertiary homoallylic alcohols has been developed. The reaction of allyltitanocenes, generated by the reductive titanation of various allylic substrates with a titanocene(II) species, with a variety of ketones produced the anti tertiary homoallylic alcohols in good diastereoselectivity, even when using sterically less congested ketones (see scheme; Cp: cyclopentadienyl; Piv: pivaloyl).The reaction of allyltitanocenes, generated by the reductive titanation of allylic sulfides or allylic alcohol derivatives with a titanocene(II) species, with phenyl and sterically hindered alkyl methyl ketones produced anti tertiary homoallylic alcohols with complete diastereoselectivity. Even when sterically less congested methyl ethyl ketone and methyl vinyl ketone were employed, the anti homoallylic alcohols were obtained with unprecedented high diastereoselectivity. The observed anti selectivity suggests that the reaction proceeds by the addition of primary (E)-sigma-allyltitanocenes to ketones through chairlike cyclic transition states.