Furan-2-yl Anions as γ-Oxo/Hydroxyl Acyl Anion Equivalents Enabled by Iridium-Catalyzed Chemoselective Reduction

Abstract

The last piece of the puzzle: Furan-2-yl anions are first demonstrated as robust γ-oxo and γ-hydroxyl acyl anion equivalents to convert aldehydes and ketones into trifunctionalized dihydroxyl ketones and hydroxyl diones through sequential nucleophilic addition, Achmatowicz rearrangement, and herein freshly established iridium-catalyzed highly selective transfer hydrogenation reduction.

Accessing para-Alkylphenols via Iridium-Catalyzed Site-Specific Deoxygenation of Alcohols

“…The mechanisms for the generation of 8 and 9 were suggested to be 1,6-elimination and 1,6-addition, respectively, of the corresponding protonated p -quinone methides B , which should resonate with the carbocation form C . Isotope tracing experiments indicated that the hydride source should be the formyl hydrogen of formic acid (Scheme c) . Also, similar to our previous work, ,, H–D exchanges between [Ir]–D and H 2 O, as well as [Ir]–H and D 2 O, were also observed.…”

“…Iridium hydride F , the transient active reducing agent, is generated by β-H elimination of iridium formate E , which should serve as the catalyst rest state during the turnover. Our and others’ previous work have clearly demonstrated that the formyl hydrogen (more hydridic) rather than the hydroxyl proton (more acidic) serves as the hydride source. , On the other hand, the substrates 1 are converted to protonated p -quinone methides B under acidic conditions. The isolation of 7 (Scheme a) indicated that the equilibrium between B and A should lie strongly on the side of A .…”

“…It would be much better if a catalytic process is developed. Fortunately, our previous work on the iridium-catalyzed transfer hydrogenations disclosed that the mechanistically involved iridium hydrides well existed in acidic media (pH as low as 1.5) , and showed enough reactivity to transfer its weakly nucleophilic hydride to various electrophiles under acidic conditions . Herein, we avail ourselves of a feasible and practical catalytic site-specific deoxygenation of 4-hydroxybenzylic alcohols (Scheme f) and provide an efficient access to 4-alkylphenols and related bioactive and natural products.…”

PyBox–La(OTf)3-Catalyzed Enantioselective Diels–Alder Cycloadditions of 2-Alkenoylpyridines with Cyclopentadiene

“…The key factor that underlies this protocol is the choice of a chiral ligand. Our previous research with didentate pyridyl imidazolines [19][20][21][22] led us to consider similar chirally modified nitrogen ligands. Considering the special coordination numbers of rare earth salts, we designed and synthesized several tridentate chiral nitrogen ligands and evaluated their chirality transfer ability in the rare earth-catalyzed Diels-Alder cycloadditions between 2-alk-2-enoylpyridines and cyclopentadiene.…”