Below is a list of refereed articles based on our exciting research findings that we have published in various scientific journals up to this date. For easier access and a cleaner look, they have been grouped by year. Simply click on the title of the article to display the toggle abstract. The full PDF version is also available by clicking on the yellow button to jump to the publisher’s web site. If you do not have a subscription agreement with these electronic journals, please contact the Charette group to request a copy directly.
A borocyclopropanation of (E)- and (Z)-allylic ethers and styrene derivatives via the Simmons-Smith reaction using a novel boromethylzinc carbenoid is described. The carbenoid precursor is prepared via a 3-step sequence from inexpensive and commercially available starting materials. This methodology allows for the preparation of 1,2,3-substituted borocyclopropanes in high yields and diastereoselectivities. Several post-functionalization reactions were also performed to illustrate the versatility of these building blocks.
This Minireview describes recent advances toward the synthesis of trifluoromethylated and difluoromethylated-substituted cyclopropanes. Synthetic methodologies using [2+1] cycloaddition, ring contraction and ring closure cyclopropanation since 2010 are reported.
Electron-rich diazo compounds, such as aryldiazomethanes, are powerful reagents for the synthesis of complex structures, but the risks associated with their toxicity and instability often limit their use. Flow chemistry techniques make these issues avoidable, as the hazardous intermediate can be used as it is produced, avoiding accumulation and handling. Unfortunately, the produced stream is often contaminated with other reagents and by-products, making it incompatible with many applications, especially in catalysis. Herein is reported a metal-free continuous flow method for the production of aryldiazomethane solutions in a non-coordinating solvent from easily prepared, bench-stable sulfonylhydrazones. All by-products are removed by an in-line aqueous wash, leaving a clean, base-free diazo stream. Three successful sensitive metal-catalyzed transformations demonstrated the value of the method.
Palladium-catalyzed direct alkenylation of cyclopropyl C-H bonds proceeds in high efficiency. This transformation provides access to novel cyclopropyl-fused azacycles. Ligand studies suggest that bisphosphine monoxide analogues of dppf and rac-BINAP are the active ligand species. Preliminary results support that both BozPhos and IPrMonophos ligands can achieve high enantioinduction for this novel direct alkenylation reaction. To date, this represents the first example of enantioselective C-H functionalization employing a bisphosphine monoxide ligand.
A fundamentally simple, mild, and practical procedure for peptide bond formation is reported that employs a stoichiometric amount of easy-to-access 9-silafluorenyl dichlorides as the coupling agent. Without initial preactivation or elaboration of the carboxylic acid or amine termini of the amino acids, the developed reagent is proposed to act through an unprecedented chemical ligation mechanism, bringing the two coupling partners together before being subsequently eliminated. The desired amides or peptide bonds are thus furnished in good yields and with low to no epimerization.
3-Aminoimidazo[1,2-a]pyridines are rapidly synthesized via a facile and mild cyclodehydration-aromatization reaction starting from readily available amides. The cyclodehydration step is mediated by the activation of N-Boc-protected 2-aminopyridine-containing amides by triflic anhydride (Tf2O) in the presence of 2-methoxypyridine (2-MeO-Py). Subsequently, the addition of K2CO3 in THF ensured a clean deprotection-aromatization sequence to afford the desired heterocycle. A wide variety of functional groups and substitution patterns were tolerated under the optimized procedure, and good to excellent yields were obtained for the fused bicyclic 3-azaheterocycles. In addition, the reaction was found to be scalable to gram-scale and could be performed with unprotected acyclic amide precursors. We also found that the resulting products were valuable intermediates for both Pd- and Ru-catalyzed C-H arylation reactions, allowing for the elaboration to diversely functionalized building blocks.
The combination of a fluorine atom and a cyclopropane ring, which both possess unique structural and chemical features, can generate new relevant scaffolds with potential interest for the synthesis of new bioactive compounds. In this review, we report the impressive progress recently devoted to the synthesis of fluorocyclopropanes especially using asymmetric methods and highlight some recent reported applications (short review).
The first in-flow difluorocarbene generation and addition to alkenes and alkynes is reported. The application of continuous flow technology allowed for the controlled generation of difluorocarbene from TMSCF3 and a catalytic quantity of NaI. The in situ generated electrophilic carbene reacts smoothly with a broad range of alkenes and alkynes, allowing the synthesis of the corresponding difluorocyclopropanes and difluorocyclopropenes. The reaction is complete within a 10-min residence time at high reaction concentrations. With a production flow rate of 1 mmol/min, continuous flow chemistry enables scale up of thisprocess in a green, atom-economic, and safe manner.
The formation of the D-homocyclopamine ring system in IPI-926 is the key step in its semisynthesis and proceeds via a chemoselective cyclopropanation followed by a stereoselective acid-catalyzed carbocation rearrangement. In order to perform large-scale cyclopropanation reactions, we developed new iodomethylzinc bis(aryl)phosphate reagents that were found to be both eff ective and safe. These soluble reagents can be prepared under mild conditions and are stable during the course of the reaction. Importantly, they have favorable energetics relative to other cyclopropanating agents such as EtZnCH2I. Herein, we describe the process optimization studies that led to successful large-scale production of the D-homocyclopamine core necessary for IPI-926.
A catalytic asymmetric synthesis of halo-cyclopropanes is described. The developed method is based on a carbenoid cyclopropanation of 2-haloalkenes with tert-butyl α-cyano-α-diazoacetate using a chiral rhodium catalyst, permitted access to a broad range of highly functionalized chiral halo-cyclopropanes (F, Cl, Br and I) in good yields, moderate diastereoselectivity and excellent enantiomeric ratios. The reported methodology represents the first general catalytic enantioselective approach to halo-cyclopropanes.
Intramolecular Pd-catalyzed functionalization of cyclopropyl α-amino acid-derived benzamides proceeds without silver or pivalate additives. Both electronically- and sterically-diverse ethyl 1,2,3,4-tetrahydroisoquinolone-3-carboxylates were accessible in good to excellent yields.