Asymmetric phase transfer Darzens reactions catalyzed by d-glucose- and d-mannose-based chiral crown ethers

Sugar-based Crown Ethers in Enantioselective Syntheses

“…Another key compound (19) was prepared by the reductive ring opening of 2,3-anhydro derivative 13 carried out with tetrabutylammonium tetrahydroborate (Bu 4 NBH 4 ) leading to the diaxial ring opening product, methyl 4,6-O-benzylidene-2-deoxy-α-d-ribo-hexopyranoside (17). Removal of the benzylidene acetal moiety in compound 17 was performed by catalytic hydrogenation to furnish methyl-2-deoxy-α-d-ribohexopyranoside (18).…”

“…5). The trans-epoxyketone (32) was obtained in general in a diastereomeric excess (de) of >98 %, with a configuration of (-)-(2R,3S) [5,8,14,[16][17][18]. The aromatic unit (Ar 1 ) of the α-chloro-carbonyl compounds (30) were phenyl-, 2-furyl-, 2-thiophenyl-, 2-pyrroyl.…”

“…The substituents of benzaldehyde used as the reactants had a significant impact on the yield and enantioselectivity (Table 3, entries 3-4 and 6-9) [17]. The α,β-epoxyketones with a furan (Table 3, entries 6-7) or a thiophene (Table 3, entries 8-10) moiety were obtained in good enantioselectivities (up to 86 % ee) as well as excellent diastereoselectivities (up to 98:2), but the epoxyketone with a pyrrole ring was formed in a low yield and enantioselectivity (Table 3, entry 11).…”

“…6). It is reasonable to assume that the other epoxyketone derivatives with negative optical rotation also possess the same 2R,3S absolute configuration [17].…”

“…7). The trans-epoxyketones (35 and 36) were obtained in good yields with high diastereoselectivites (de of >98 %) and with moderate to good enantioselectivities [14,17]. The reaction of 2-chloro-1-indanone (33) and benzaldehyde gave epoxyketone 35a (Ar = Ph) in a yield of 59 % and in an ee value of 65 %.…”