Daniel Farran

Diastereoselective Synthesis of 2,3,4,5,6-Pentafluoroheptanes

A stereocontrolled synthesis of alkanes containing five contiguous fluorine atoms is presented. The compounds were prepared by sequential fluorination of diastereoisomeric alcohol-diepoxides. The chemistry involved epoxide ring-opening with HF.NEt(3) and deshydroxyfluorination reactions of free alcohols with Deoxo-Fluor. The fluorination reactions were all highly stereospecific, with all five fluorines being incorporated in three sequential steps. Three different diastereoisomers of the 2,3,4,5,6-pentafluoroheptyl motif were prepared as heptane-1,7-diol derivatives, a structural format amenable for incorporation of the vicinal pentafluoro scaffold into larger molecular architectures.

Regioselective and sequential reactivity of activated 2,5‐diketopiperazines

The electrophilic reactivity of Boc‐DKPs has been studied. Thanks to Boc activation, the opening ability of carbonyl lactam groups is enhanced. According to experimental conditions, this enabled the synthesis of Boc‐amino acid derivatives or original dipeptides via a regioselective and sequential way. Copyright

Access to N-Thioalkenyl and N-(o-Thio)aryl-benzimidazol-2-ones by Ring Opening of Thiazolobenzimidazolium and Benzimidazobenzothiazolium Salts and C–O Bond Cleavage of an Alkoxide

We report herein the synthesis of highly functionalized 1,3-dihydro-2H-benzimidazol-2-ones via a ring opening of thiazolo[3,2-a]benzimidazolium or benzimidazo[2,1-b][1,3]benzothiazol-6-ium salts and an unusual C-O bond cleavage of an alkoxide. A large variety of benzimidazolones bearing an original N-thioalkenyl or N-(o-thio)aryl group was obtained in high yields. The developed chemistry provides efficient and rapid access to the privileged benzimidazol-2-one scaffold.

Hammet Constants Effects in Microwave Cascade Etherification-Cyclization-Krapcho Reaction to Access [2,3]-Dihydrobenzofuran-3-ones from Salicylic Derivatives

Abstract Two methods were evaluated for the synthesis of substituted [2,3]-dihydro-2-methyl-benzofuran-3-ones from corresponding salicylate esters under microwave irradiation. A two-step sequence via ether intermediates was convenient for various substituted salicylate derivatives, while the second strategy involving a one-pot procedure was efficient for electron-donating substituted salicylates. Results allowed correlation of the Hammett constants effects in the intramolecular cyclization of O-ethoxycarbonyl ether of salicylic esters. GRAPHICAL ABSTRACT

Steric scale of common substituents from rotational barriers of N-(o-substituted-aryl)-thiazoline-2-thione atropisomers

A steric scale of 20 recurrent groups was established from comparison of rotational barriers on N-(o-substituted aryl)thiazoline-2-thione atropisomers. The resulting energy of activation ΔG⧧rot reflects the spatial requirement of the ortho substituent borne by the aryl moiety, electronic aspects and external parameters (temperature and solvent) generating negligible contributions. Concerning divergent rankings reported in the literature, the great sensitivity of this model allowed us to show unambiguously that a methyl appears bigger than a chlorine and gave the following order in size: CN > OMe > OH. For the very bulky CF3 and iPr groups, constraints in the ground state decreased the expected ΔG⧧rot values resulting in a minimization of their apparent sizes.

Atropisomerism in a 10-Membered Ring with Multiple Chirality Axes: (3Z,9Z)-1,2,5,8-Dithiadiazecine-6,7(5H,8H)-dione Series

For the first time, chirality in (3 Z,9 Z)-1,2,5,8-dithiadiazecine-6,7(5 H,8 H)-dione series was recognized. Enantiomers of the 4,9-dimethyl-5,8-diphenyl analogue were isolated at room temperature, and their thermal stability was determined. X-ray crystallography confirmed the occurrence of a pair of enantiomers in the crystal. Absolute configurations were assigned by comparing experimental and calculated vibrational/electronic circular dichroism spectra of isolated enantiomers. A distorted tesseract (four-dimensional hypercube) was used to visualize the calculated enantiomerization process, which requires the rotation around four chirality axes. Conformers of higher energy as well as several concurrent pathways of similar energies were revealed.