Double asymmetric induction in 1,3-dipolar cycloaddition of five-membered cyclic nitrones to 2-(5H)-furanones

Synthesis of pyrrolizidine alkaloids via 1,3-dipolar cycloaddition involving cyclic nitrones and unsaturated lactones

“…It has been reported, however, that the cycloaddition of 18 and 2 leads to the mixture of two exo adducts 19 and 20 (Scheme 2) in a ratio of about 9:1. 7 Moreover, the reduction of lactone 19 gave diol 21 with two difficult to discriminate primary hydroxyl groups. Silylation of 21 with equimolar amount of t-BuPh 2 SiCl, or its acylation with equimolar amount of PivCl led in both cases to the mixture of substrate 21, double-substituted compound 22 (23) and two mono-substituted 24 and 25 (26 and 27), which could not be easily separated into pure regioisomers (Scheme 2).…”

“…4, 5.7 Hz, H-3 0 ), 1.61 (3H, s, CH 3 C@O), 1.20 (9H, s, t-Bu), 1.16 (9H, s, t-Bu), 1.04 (9H, s, t-Bu); 13 C NMR (125 MHz, C 6 D 6 ) d: 177. 7,169.6,81.4,79.1,77.5,73.8,73.5,70.7,63.4,59.7,58.7,48.2,38.9,29.0,28.5,27.3,20.5;HRMS (ESI): calcd for C 23 H 42 NO 6 : 428.3007 [M+H + ], found: 428.3027.…”

“…(2S,3S,3aS,4S,5S)-2,3-Bis(pivaloyloxymethyl)-4,5-di-tertbutoxy-hexahydropyrrolo[1, 2-b]isoxazol (23) [a] D +37.8 (c 0.95, CH 2 Cl 2 ); IR (film) m: 1730 cm À1 ; 1 H NMR (500 MHz, C 6 D 6 ) d: 4.54 (1H, dd, J 11.6, 3.5 Hz, C 2 CHHOPiv), 4.46 (1H,ddd,J 7.6,6.3,3.5 Hz,4.27 (1H,dd,J 11.6,7.6 Hz, C 2 CHHOPiv), 4.22-4.12 (2H, C 3 CH 2 OPiv), 3. 85-3.78 (2H, m, H-4, H-5), 3.60 (1H, dd, J 11.9, 5.1 Hz, H-6), 3.50 (1H, dd, J 3.9, 3.7 Hz, H-3a), 3.06 (1H, dd, J 11.9, 5.0 Hz, H-6 0 ), 2.82-2.73 (1H, m, J 7.2, 6.3, 6.3, 3.9 Hz, H-3), 1.23 (9H, s, t-Bu), 1.19 (9H, s, t-Bu), 1.14 (9H, s, t-Bu), 1.01 (9H, s, t-Bu); 13 C NMR (125 MHz, C 6 D 6 ) d: 177.…”

“…The corresponding transformations involving c-lactones proceed with a lower diastereoselectivity, as compared with the cycloaddition to the six-membered ones due to the possible formation of endo adducts. 7 A single adduct is formed only in the case of the matching pair when the endo approach of reactants is hindered. Cycloadducts 4 and 5 readily available from the D-glycero lactone 1 and nitrones of L-(+)-tartaric acid 2 and D-(+)-malic acid 3, respectively, are particularly attractive.…”

Synthesis of iminosugars via 1,3-dipolar cycloaddition reactions of nitrones to α,β-unsaturated sugar aldonolactones

“…To expand our studies on 1,3-dipolar cycloadditions involving unsaturated lactones, we directed our attention towards the use of cyclic nitrones 10-16 in these reactions [56][57][58][59][60][61][62]. The attractiveness of cyclic dipoles as synthons in a target-oriented synthesis has been proven repeatedly [10,27,31,63].…”