Regioselective Benzoylation of Glycopyranosides by Benzoyl Chloride in the Presence of MoO₂(acac)₂

Total Synthesis of the Potent and Broad-Spectrum Antibiotics Amycolamicin and Kibdelomycin

“…Benzylation of the C1−OH of L-rhamnose (6, BnOH, NH 2 SO 3 H, 82%) 13 followed by a regioselective acetylation of C3−OH with AcCl in the presence of MoO 2 (acac) 2 (2 mol %) afforded 13 (79%). 14 To methylate the C2−OH and invert the configuration of C4−OH, a selective oxidation of C4−OH using Waymouth's Pd catalyst (14, 5 mol %) under an O 2 atmosphere achieved 78% yield. 15 Note that this Pd catalyzed oxidation was initially developed for the selective oxidation of the C3−OH of pyranosides.…”

“…The syntheses of the three fragments 2 – 4 are outlined in Scheme . Benzylation of the C1–OH of l -rhamnose ( 6 , BnOH, NH 2 SO 3 H, 82%) followed by a regioselective acetylation of C3–OH with AcCl in the presence of MoO 2 (acac) 2 (2 mol %) afforded 13 (79%) . To methylate the C2–OH and invert the configuration of C4–OH, a selective oxidation of C4–OH using Waymouth’s Pd catalyst ( 14 , 5 mol %) under an O 2 atmosphere achieved 78% yield .…”

Regioselective modification of unprotected glycosides

“…Other systems for the regioselective protection of diols have been reported based on organoboron, [46][47][48] organosilicon, 49,50 copper(II), [51][52][53][54][55] silver(I), 56 nickel(II) 57 and molybdenum(V) and (II) ( Table 2). 58,59 These systems show often a similar selectivity as observed in tin mediated protections. This could indicate that the selectivity also depends on stereo-electronic effects in the carbohydrate 45 or as mentioned before solely depends on steric interactions between the carbohydrate and electrophile.…”

Boronic Acid-Catalyzed Final-Stage Site-Selective Acylation for the Total Syntheses of <i>O</i>-3′-Acyl Bisabolol β-D-Fucopyranoside Natural Products and Their Analogues

“…[3][4][5][6] Polyols with many hydroxy groups represented by carbohydrates are ubiquitous in nature and often have a structure in which only a part of the hydroxy groups is acylated. Thus far, there are many examples of site-selective acylation of carbohydrates using metal complex catalysts (e.g., chiral copper, 7,8) organotin, 9) molybdenum complex, 10) and iron 11) ) and organocatalysts (e.g., chiral 4-pyrrolidinopyridine, 12,13) peptides, 14) chiral imidazole, 15) chiral N-heterocyclic carbene (NHC), 16) chiral benzotetramisole (BTM), 17) borinic acid, 18) and benzoxaborole 19) ). In fact, there are reports in which site-selective acylation has been considered a powerful means for synthesizing partially acylated polyol natural products with focus on structure-activity relationships.…”