Organocatalytic Redox Deracemization of Cyclic Benzylic Ethers Enabled by An Acetal Pool Strategy

Abstract

The first redox deracemization of a series of cyclic benzylic ethers, including 6H-benzo[c]chromenes, isochromans, and 1H-isochromenes, is described. An "acetal pool" strategy was adopted to harmonize the complete oxidation of secondary ethers with imidodiphosphoric acid catalyzed asymmetric transfer hydrogenation. The synthetic utility of the process was demonstrated by the effective deracemization of biologically active molecules of interest that are difficult to prepare by other methods.

Oxidative Dearomative Cross-Dehydrogenative Coupling of Indoles with Diverse C-H Nucleophiles: Efficient Approach to 2,2-Disubstituted Indolin-3-ones

“…However, when C-3 substituted indoles such as 3-methylindole, melatonine, and tryptamine derivative were subjected to the reaction, the expected 2,2 -bisindolin-3-ones 5r-5t were obtained in low yields. Excitingly, MeOH as an additive proved to be beneficial and enhanced the reactivity of the reaction, and satisfying yields (90-92%) of coupling products were achieved [89][90][91][92][93]. Molecules 2020, 25, x FOR PEER REVIEW 5 of 22 [a] 5 equiv MeOH was employed as additive.…”

Deracemisation Processes Employing Organocatalysis and Enzyme Catalysis

“…This additive enables the conversion of the racemic ether 31 into the acetal 32 , which in the presence of a chiral Brønsted acid catalyst would lead to the chiral ion pair 33 , and then asymmetric hydrogen transfer through chiral anion catalysis would afford the desired ( R )‐ 31 . Thus, initial experiments were performed in the deracemisation of 6 H ‐benzo[ c ]chromene ( 31a , Scheme a), a motif occurring in the structure of different valuable compounds . Hantzsch ester IIIa and a chiral phosphoric acid were employed in the asymmetric hydrogenation.…”

“… a) Organocatalysed deracemisation of 6 H ‐benzo[ c ]chromene. b) Deracemisation of 1,3,4,9‐tetrahydropyrano[3,4‐ b ]indoles by using DDQ and a chiral phosphoric acid …”

Alkynyl Coinage Metal Clusters and Complexes–Syntheses, Structures, and Strategies

“…Each of the two central silver atoms forms an early linear arrangement with two alkynides coordinated in the typical m 2 -h 1 mode.F urthermore, these alkynides stabilizet he apical silver atoms througha na symmetric h 2 coordination.W hile in both complexes 25 and 26 the four silver atoms are arranged in an early planar structure,t he apical Ag I positions of the latter are only coordinated by one PCy 3 ligand ( Figure 15 aand c), presumably due to the larger steric demand of the cyclohexylphosphine ligand.N onetheless, the coordination of the alkynyl ligand is an identical m 2 -h 1 type in both complexes. The tetranuclears ilver(I) clusters 25 and 26 structurally vary from the tetranuclear Cu I complex 5 [Cu(CCPh)(PPh 3 )] 4 , [52] but show similarities to the rhomboidal gold complex 51,d escribed later.I nterestingly, the sterically less demanding phenylbutadiynyl gives in the reaction of PCy 3 and [Ag(CCÀCCPh)] n in dichloromethane a structurally different tetranuclear complex [Ag(CCÀC CPh)(PCy 3 )] 4 (27) ( Figure 15 band d). [81] The molecular structure of complex 27 contains four silver atoms and four phenylbutadiynyl ligands coordinating regularly to each corner of the distorted cubane structure in a m 2 -h 1 h 2 coordination mode.…”

“…[23,24] Recently,l arger metal nanoclusters have been stabilized by exclusively alkynyl ligands, giving well-defined structures and compositions. [25][26][27][28][29][30][31][32][33] For these alkynyl-stabilized metal nanoclusters the labile nature of alkynyl ligands was further explored, andf acile removal (exchange) under mild conditions was demonstrated whilst maintaining their core structure. [26] The structural variability of the alkynylligands, the possibility to use ancillary ligands, and templating effects offer large chemicald iversity and has resulted in am yriado fs tructural motifs displaying numerousi nteresting structural, optical, electronic, and responsive properties.…”