A class of monomeric nuphar analogues that are either epimeric at C1 and C1′ or lack the naturally occurring methyl group at those positions were synthesized and evaluated for biological activity. The syntheses feature enantioselective vinylogous Mukaiyama–Mannich (vM–Mannich) reactions catalyzed by chiral phosphoric acids that proceed with excellent diastereoselectivity. Biological assays reveal that both the desmethyl and C1-epimeric monomeric nuphar analogous are able to induce rapid apoptosis.

Herein, we report the first examples of the synthesis of pyrroloindolines by means of (3 + 2) dearomative annulation reactions between 3-substituted indoles and highly reactive azaoxyallyl cations. Computational studies using density functional theory (DFT) (B3LYP-D3/6-311G**++) support a stepwise reaction pathway in which initial C–C bond formation takes place at C3 of indole, followed by ring closure to give the observed products. Insights gleaned from these calculations indicate that the solvent, either TFE or HFIP, can stabilize the transition state through H-bonding interactions with oxygen of the azaoxyallyl cation and other relevant intermediates, thereby increasing the rates of these reactions.

An In(III)-catalyzed vinylogous addition of O-silyl vinylketene acetals to 2,3-dihydro-4-pyridinones has been developed. The method features the unprecedented employment of supersilyl groups to influence the γ versus α regiochemical control of vinylogous Mukaiyama–Michael (vM−Michael) reactions when γ-substituted O-silyl vinylketene acetals are used. We also demonstrate that these reactions allow facile access to quinolizidine-based alkaloids such as deoxynupharidine and well as lasubine I and II.

A diastereoselective (3 + 2) dearomative annulation of 3-substituted indoles with α-haloketones has been developed. Significant regiochemical control was observed. This methodology provides easy access to highly functionalized cyclopenta- or cyclohexa-fused indoline compounds, which are common structures of many natural products. The synthetic potential of this reaction was demonstrated in the concise syntheses of the core structures of vincorine, isocorymine, and aspidophylline A. DFT studies (B3LYP-D3/6-311++G**/MeOH) on cyclization mechanisms involving the 2-hydroxyallyl cation and its deprotonated oxyallyl cation have been performed. Under the reaction conditions, with a sparingly soluble Na2CO3 base, both species may be present and both pathways are viable. Both pathways support the formation of the experimentally observed O-bound intermediate, its transformation to the final product, the regiochemical and eventual stereochemical outcome of the kinetic cyclization product, and the thermodynamic preference for formation of the final stereoisomer.

1-Phenyl-1H-tetrazole-5-thiol 1 (PT-thiol) is employed in a unique Markovnikov-selective formal hydroamination of styrenyl compounds in the presence of catalytic amounts of Ga(OTf)3. This gives rise to the formation of tetrazolothione moieties in an atom-economical manner. Mechanistically, we have determined that this transformation may occur by kinetically favored hydrothiolation, followed by rearrangement to the observed hydroamination products.

Because of the broad utility of organofluorine compounds, efficient nucleophilic fluorination reactions are of high synthetic value. This is because fluoride is generally less costly, more readily available as its positron-emitting isotope (18F−), and has a higher specific activity than its ‘F+’ counterparts. New reactions for the construction of CF bonds, that make use of contemporary chemical methods, have only lately begun to emerge. This review provides a brief summary of some of the recent disclosures in transition metal-catalyzed fluorination reactions at sp3-hybridized carbon centers with nucleophilic fluoride sources.Figure optionsDownload full-size imageDownload as PowerPoint slide

BT-sulfones react with aromatic aldehydes to furnish trisubstituted alkenes with excellent Z stereoselectivity. These sulfones are synthesized by hydrothiolation of styrene and styrenyl derivatives (followed by oxidation). This method provides a conceptually novel way to prepare these important sulfur compounds.

The convenient preparation of chiral tetrahydrothiophenes (THTs) in high enantiopurity via phosphorothioic acids and related compounds is reported. We consider these to be safer alternatives to the use of H2S which is a highly toxic gas. Each of the THTs is derived from a common intermediate, thereby greatly enhancing the flexibility of the synthesis. The key transformation is a base-promoted, intramolecular, carbon–sulfur bond-forming event. These reactions are highly stereospecific as they operate through a double SN2 displacement mechanism. The methodology is amenable to a broad array of functional groups and heterocycles. The tetrahydrothiophene motif is important because it is present in a number of bioactive natural products. They have also been utilized to promote various asymmetric transformations including hydrogenation, epoxidation, cyclopropanation, and aziridination reactions.

A highly regioselective, Pd-catalyzed allylic fluorination of phosphorothioate esters is reported. This chemistry addresses several limitations of previously reported methods in which elimination and lack of reactivity were problematic. Preliminary mechanistic investigations reveal that these reactions are stereospecific and provide fluorinated products with net retention of stereochemical configuration. In analogy to other Pd-catalyzed allylic substitution reactions, this process likely proceeds through a palladium π-allyl intermediate.

Regiocontrol of allylic alkylation reactions involving hard nucleophiles remains a significant challenge and continues to be an active area of research. The lack of general methods in which α-alkylation is favored underscores the need for the development of new processes for achieving this type of selectivity. We report that Cu(I) catalyzes the allylic substitution of phosphorothioate esters with excellent α-regioselectivity, regardless of the nature of the Grignard reagent that is used. To the best of our knowledge, the Cu-catalyzed allylic alkylation of phosphorothioate esters has never been described. We have also developed a simple protocol for inducing high α selectivity starting from secondary allylic halides. This is accomplished by using sodium phosphorothioates as an additive.

A mild two-step process for the regioselective, transition-metal-free preparation of carbon−carbon bonds from allylic alcohols/ethers and Grignard reagents is described. This process obviates the need for the harsh deprotection conditions usually required for removal of methyl ethers. The synthesis is accomplished by photochemically promoted allylic substitution reactions of allylic alcohols and ethers with diethylphosphorothioic acid followed by sp3−sp3 or sp2−sp3 bond formation with various Grignard reagents under transition-metal-free conditions. Depending on the nature of the nucleophile, the regioselectivity of the carbon−carbon bond-forming event can be controlled to furnish either quaternary or tertiary carbon centers.

It is reported that Ga(OTf)3 catalyzes the direct displacement of alcohols with sulfur nucleophiles. The products are versatile intermediates that can be utilized in carbon−carbon, carbon−sulfur bond formation or used in modified Julia olefination reactions. The only byproduct generated is water.

The synthesis of allylic thioethers arising from the reaction between phosphorothioate esters and alcohols is described. The synthesis is accomplished in one step by the addition of an exogenous alkoxide to the corresponding allylic phosphorothioate ester. It is demonstrated that this process is amenable to various functional groups and a wide variety of heterocycles. In contrast to conventional methods for thioether synthesis, no malodorous sulfur compounds such as thioacetic acid or thiols are required.