Mild Aliphatic and Benzylic Hydrocarbon C–H Bond Chlorination Using Trichloroisocyanuric Acid

We present the controlled monochlorination of aliphatic and benzylic hydrocarbons with only <i>1 equiv</i> of substrate at 25–30 °C using <i>N</i>-hydroxyphthalimide (NHPI) as radical initiator and commercially available trichloroisocyanuric acid (TCCA) as the chlorine source. Catalytic amounts of CBr₄ reduced the reaction times considerably due to the formation of chain-carrying ·CBr₃ radicals. Benzylic C–H chlorination affords moderate to good yields for arenes carrying electron-withdrawing (50–85%) or weakly electron-donating groups (31–73%); cyclic aliphatic substrates provide low yields (24–38%). The products could be synthesized on a gram scale followed by simple purification via distillation. We report the first direct side-chain chlorination of 3-methylbenzoate affording methyl 3-(chloromethyl)­benzoate, which is an important building block for the synthesis of vasodilator taprostene

Copper(I)-Catalyzed Formal Carboboration of Alkynes: Synthesis of Tri- and Tetrasubstituted Vinylboronates

The first copper-catalyzed formal carboboration of alkynes, in which a C–B bond and a C–C bond are created in a single catalytic cycle, is presented. The reaction proceeds with high regioselectivity and <i>syn</i>-stereoselectivity to form tri- and tetrasubstituted vinylboronic esters from commercially available bis­(pinacolato)­diboron. A subsequent cross-coupling reaction gives access to highly substituted alkenes

Asymmetric Nucleophilic Monofluorobenzylation of Allyl and Propargyl Halides Mediated by a Remote Sulfinyl Group: Synthesis of Homoallylic and Homopropargylic Fluorides

Fluorinated 2-(<i>p</i>-tolylsulfinyl)­benzyl carbanions react with allyl and propargyl halides in a highly stereoselective way, providing homoallylic and homopropargylic fluorides, respectively, with high optical purity. Theoretical calculations found transition states for these transformations whose relative stabilities are consistent with the experimentally observed stereoselectivity

Asymmetric Intramolecular Pauson–Khand Reaction Mediated by a Remote Sulfenyl or Sulfinyl Group

In this work, we report the use of the asymmetric intramolecular Pauson–Khand reactions of 4-aryl-4-cyano-1,6-enynes for obtaining enantiomerically enriched bicyclo[3.3.0]­octenones, and the influence of both the quaternary stereocenter and the sulfur functions located at <i>ortho</i>-position of the aryl group, on their stereoselectivity and reactivity. The sulfenyl derivatives bearing substituted or unsubstituted triple bonds and mono- and disubstituted alkene moieties afford bicyclo[3.3.0]­octenones in high yields with complete diastereocontrol. These results are explained by assuming the association of the lone electron pair at sulfur to the Co–alkyne complexes

Copper-Catalyzed Diastereo- and Enantioselective Desymmetrization of Cyclopropenes: Synthesis of Cyclopropylboronates

A novel Cu-catalyzed diastereo- and enantioselective desymmetrization of cyclopropenes to afford nonracemic cyclo­propyl­boronates is described. Trapping the cyclo­propyl­copper intermediate with electrophilic amines allows for the synthesis of cyclo­propyl­amino­boronic esters and demonstrates the potential of the approach for the synthesis of functionalized cyclopropanes

Control of the Dual Reactivity (Iminium-Dienamine) of β‑Arylmethyl α,β-Unsaturated Aldehydes in Organocatalytic 1,3-Dipolar Cycloadditions with <i>N</i>‑Benzoyl <i>C,N</i>-Cyclic Azomethine Imines

1,3-Dipolar cycloadditions of <i>C,N</i>-cyclic azomethine imines with α,β-unsaturated aldehydes can be performed with complete control of the regio-, <i>exo</i>-, and enantioselectivity under aminocatalytic conditions. The so far never studied competence of the iminium-dienamine reactivity inherent to β-alkyl α,β-unsaturated aldehydes was studied, which was possible by allowing achievement of complete control of the chemoselectivity in reactions of the β-arylmethyl derivatives with azomethine imines by using different additives and organocatalysts, whose role has been rationalized by DFT calculations and chemical proofs. Thus, it has been possible to selectively obtain the pyrazolidines resulting from both the attack to the C2–C3 (via iminium) and the C3–C4 (via dienamine) bonds at the starting enals, which can be used as precursors of interesting tetrahydroisoquinolinic compounds

Copper-Catalyzed Borylative Aromatization of <i>p</i>‑Quinone Methides: Enantioselective Synthesis of Dibenzylic Boronates

In this report, we establish that DM-Segphos copper­(I) complexes are efficient catalysts for the enantioselective borylation of <i>para</i>-quinone methides. This method provides straightforward access to chiral monobenzylic and dibenzylic boronic esters, with enantiomeric ratios up to 96:4, using a commercially available chiral phosphine. Standard manipulations of the C–B bond afford a variety of chiral diaryl derivatives