Diastereoselection in 1,3-dipolar cycloadditions of a chiral cyclic nitrone to α,β-unsaturated δ-lactones

Kinetic Resolutions by Means of Cycloaddition Reactions

“…[31] The high facial differentiation of the double bond of the lactone is due to the presence of the C 6 acetoxymethyl group. Indeed, in the case of (R)-35, the exo approach of the dipolarophile proceeds syn with respect to the C 6 acetoxymethyl group (approach mode B, Figure 5) and it is therefore disfavoured, resulting in efficient kinetic resolution of the racemate.…”

“…Indeed, cycloaddition between 30c and achiral lactone 34 occurred with almost total regio-and stereoselectivity, producing the exo-anti adduct 37 (Scheme 9) [31] and once more confirming the high facial diastereoselection of nitrone 30c.…”

“…[30] Double asymmetric induction in 1,3-dipolar cycloadditions of 30c with sugar-derived α,β-unsaturated lactones has recently been investigated. [31] Hexopyranoid α,β-unsaturated lactones such as the readily available -glycero-derived (S)-35 [32] and -threo-36 [33] (Scheme 8) showed high facial diastereoselectivities towards conjugate additions of hydroxylamines [34] and hydrazines, [35] undergoing conjugate addition exclusively anti to the acetoxymethyl group. The high diastereoselectivity in the reactions of α,β-unsaturated cyclic ketones has been interpreted by invoking preferred axial approach of nucleophiles, resulting in more stable, chair-like enolate intermediates.…”

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].…”

Synthesis of 1-homoaustraline

“…[1][2][3] In the case of mismatched pairs (syn either to acetoxymethyl or to 3-tert-butoxy group), the 4-O-acetyl group of the lactone assumes a decisive role in the control of the stereochemical outcome of the cycloaddition. This stereochemical preferences leads, in many cases, to formation of a single adduct or at least a high preponderance of a single adduct.…”