This work describes the first example of using chiral catalysts to control site-selectivity for the glycosylations of complex polyols such as 6-dEB and oleandomycin-derived macrolactones. The regiodivergent introduction of sugars at the C3, C5 and C11 positions of macrolactones was achieved by selecting appropriate chiral acids as catalysts or through introduction of stoichiometric boronic acid-based additives. The BINOL-based CPAs were used to catalyze highly selective glycosylations at the C5 positions of macrolactones (up to 99:1 rr) whereas the use of SPINOL-based CPAs resulted in selectivity switch and glycosylation of the C3 alcohol (up to 91:9 rr). Additionally, the C11 position of macrolactones was selectively functionalized through traceless protection of the C3/C5 diol with boronic acids prior to glycosylation. The investigation of the reaction mechanism for the CPA-controlled glycosylations revealed the involvement of covalently linked anomeric phosphates rather than oxocarbenium ion pair as the reactive intermediates.
A thiophosphoramide-based co-catalyst was found to significantly accelerate copper(II) trifluoromethanesulfonate-catalyzed arylation of potassium carboxylates with diaryliodonium salts. This effect could be attributed to counterion activation of diaryliodonium salts or organocopper intermediates by thiophosphoramides. Inclusion of thiophosphoramides permits achieving significantly milder reaction conditions and expands the scope of solvents and diaryliodonium counterions that could be used for the arylation of carboxylate nucleophiles.
A direct single-step hydrogenation of BINOL-based chiral phosphoric acids, N-triflyl phosphoramides, and disulfonimides to the corresponding H8-BINOL Brønsted acids in excellent yields and chemoselectivities is described. In addition, the conditions for the single-step oxidation of H8-BINOL-based Brønsted acids into the corresponding BINOL-based acids have been identified and employed to accomplish these interconversions in 41-81% yield.
A simple and reliable protocol for determining the enantiopurity of 3,3′-substituted BINOL-and H8-BINOL-based chiral phosphoric acids (CPA) using 31 P NMR spectroscopy in the presence of chiral amines as the discriminating agents is described. The generality of this method is demonstrated using nine common BINOL-and H8-BINOLbased chiral acids. This technique was utilized for monitoring the extent of racemization of 3,5-(F 3 C) 2 C 6 H 3 -substituted BINOL-and H8-BINOLbased CPA at 200, 220, and 250 °C.
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