2,3-Unsaturated Allyl Glycosides as Glycosyl Donors for Selective α-Glycosylation

Abstract

In the presence of NBS and a catalytic amount of a Lewis acid, 2,3-unsaturated allyl glycosides [6-(allyloxy)-3,6-dihydro-2-(hydroxymethyl)-2H-pyran-3-ol] have been successfully used as versatile glycosyl donors for the stereoselective α-glycosylation of a variety of alcohols comprising sensitive functions such as acetonide, keto, nitro, and ester in 50-90% yields. The methodology offers an equally facile alternative to 4-pentenyl replacement in unsaturated sugars.

A Survey of Recent Synthetic Applications of 2,3-Dideoxy-Hex-2-enopyranosides

“…Taneja and co-workers recently described the remarkable stereoselective α-glycosylation of 2,3-unsaturated allyl glycosides mediated by NBS in the presence of catalytic Zn(OTf) 2 [163]. The method was applied to the glycosylation of a variety of alcohols with erythro - and threo - 2,3-unsaturated allyl glycosides 197 and 198 , respectively (Scheme 47).…”

“…A series of synthetic transformations of de novo hex-2,3-enopyranose derivatives, e.g., 155 , into a variety of monosaccharide and deoxy-monosaccharide derivatives have been described by O’Doherty’s group [167]. These transformations make imaginative use of addition, oxidation, and substitution reactions performed on hex-2,3-enopyranoses and 3,4-unsaturated pyranoses, e.g., 207 , the latter readily available from the former by Wharton rearrangement (Scheme 49) [168]. Accordingly, Boc-pyranone 155 was converted by way of stereoselective Pd(0) glycosylation into α-benzyl derivative 205 , whose epoxidation under basic conditions led stereoselectively to epoxy ketone 206 [169].…”

Synthesis of 2-C-Branched Sugars

“…Spectral data matched those which have been previously reported 108. R f = 0.35 (9:1 hexanes:ethyl acetate);1 H NMR: (CDCl 3 ) δ H 7.32-7.20 (complex m, 15H, Bn), 6.05 (d, J = 10.3 Hz, 1H, H-3), 5.76 (ddd, J = 10.3, 2.6, 2.2 Hz, 1H, H-2), 5.10 (d, J = 2.2 Hz, 1H, H-1), 4.78 (d, J = 11.7 Hz, 1H, PhCH 2 ), 4.62 (d, J = 12.2 Hz, 1H, PhCH 2 ), 4.57 (d, J = 11.6 Hz, 1H, PhCH 2 ), 4.56 (d, J = 12.7 Hz, 1H, PhCH 2 ), 4.48 (d, J = 12.2 Hz, 1H, PhCH 2 ), 4.41 (d, J = 11.6 Hz, 1H, PhCH 2 ), 4.16 (ddd, J = 9.5, 3.1, 1.7 Hz, 1H, H-4), 3.97 (apparent dq, J = 9.5, 2.0 Hz, 1H, H-5), 3.69 (dd, J = 10.6, 4.1 Hz, 1H, H-6a), 3.60 (dd, J = 10.6, 2.0 Hz, 1H, H-6b); 13 C NMR: (CDCl 3 ) δ C 138.3 (C, Bn), 138.19 (C, Bn), 138.17 (C, Bn), 130.9 (CH, C-3), 128.50 (CH, Bn), 128.49 (CH, Bn), 128.46 (CH, Bn), 128.45 (CH, Bn), 128.1 (CH, Bn), 128.0 (CH, Bn), 127.93 (CH, Bn), 127.86 (CH, Bn), 127.7 (CH, Bn), 126.6 (CH, C-2), 94.1 (CH, C-1), 73.5 (CH 2 , PhCH 2 ), 71.2 (CH 2 , PhCH 2 ), 70.5 (CH, C-4), 70.2 (CH 2 , PhCH 2 ), 69.4 (CH, C-5), 68.9 (CH 2 , C-6); IR (Film from CH 2 Cl 2 ): ν max 3063, 3030, 2865, 1496, 1454, 1094, 1071, 1039, 1025, 733, 696 cm −1 ; HRMS: m/z C 27 H 28 O 4 Na + [M+Na] + calcd 439.1885, found 439.1883.…”

“…106, 107) have gained prominence as activated boron reagents. These compounds can be synthesised through the addition of dialkylborane to alkynes (108) or alkenes (109) in a hydroboration reaction, followed by treatment with KHF 2 in acetone. The hydroboration reaction proceeds through a cis-anti-Markovnikov addition as shown in Scheme 1.30.…”

Glycosylations of Glycals using N-Iodosuccinimide (NIS) and Phosphorus Compounds for Syntheses of 2-Iodo- and 2-Deoxyglycosides

“…Cyclohexylmethyl 3,4,6-Tri-O-benzyl-2-deoxy-2-iodo-β-D-glucopyranoside (3aβ). The anomeric mixture was purified by flash column chromatography (10 g, n-hexane/EtOAc 8/1) to give compound 3aβ (9.2 mg, 23%): white solid; R f 0.42 (8/1 n-hexane/EtOAc); [α] 25 D +25.4°(c 1.33, CHCl 3 ); mp 66−67 °C; 1 H NMR (500 MHz, CDCl 3 ) δ 7.43−7.41 (2H, m), 7.34−7.27 (11H, m), 7.20−7.17 (2H, m), 4.98 and 4.85 (2H, ABq, J = 10.1 Hz), 4.79 and 4.57 (2H, ABq, J = 10.9 Hz), 4.61 and 4.55 (2H, ABq, J = 12.0 Hz), 4.50 (1H, d, J = 8.9 Hz), 3.92 (1H, dd, J = 8.9 and 10.9 Hz), 3.76−3.68 (4H, m), 3.60 (1H, dd, J = 8.6 and 9.7 Hz), 3.49 (1H, ddd, J = 2.3, 4.6, and 9.7 Hz), 3.29 (1H, dd, J = 7.2 and 9.2 Hz), 1.92−1.61 (6H, m), 1.29−1.13 (3H, m), 1.02−0.93 (2H, m); 13 C NMR (125 MHz, CDCl 3 ) δ 138. 1, 137.7, 128.5, 128.4 × 2, 128.1, 127.9, 127.7, 127.6, 103.3, 85.9, 79.7, 76.0, 75.5, 75.2, 74.9, 73.5, 68.6, 37.8, 33.1, 30.1, 29.8, 26.6, 25.8 × 2; HRMS (ESI-TOF) m/z [M + Na] + calcd for C 34 H 41 IO 5 Na 679.1896, found 679.1888. n-Octyl 3,4,6-Tri-O-benzyl-2-deoxy-2-iodo-α-D-glucopyranoside (3bα).…”