diphenylhydroxyselenium acetate and iodine under visible light irradiation generated the anomeric radical 343, which underwent a β-fragmentation of the C1–C2
bond to afford the C2 radical 344. Oxidation of intermediate radical 344 with the
reagent gave oxonium ion 345, which reacted intramolecularly with the nucleophilic carboxyl group to furnish a separable anomeric mixture of 5,1-lyxuronic acid
lactone 346.
A general method for the synthesis of γ-acyl-δ-lactones has been developed by
Lugan et al. by vicinal di-functionalization of α,β-unsaturated ketones via manganese carbene intermediates [125] (Scheme 78). Treatment of manganese carbene
347 with n-BuLi generated the carbene anion, which underwent Michael addition
with benzylidene acetone and chalcone to give carbene-enolate intermediate 349. A
cascade aldolization/transesterification of this intermediate with benzaldehyde
afforded the oxacyclocarbene complexes 350, which were readily oxidized by air
to release γ-acyl-δ-lactone 351.
Scheme 77 Synthesis of alduronic acid lactones
Scheme 78 Synthesis of γ-acyl-δ-lactones
Synthesis of Saturated Six-Membered Ring Lactones
135
bond to afford the C2 radical 344. Oxidation of intermediate radical 344 with the
reagent gave oxonium ion 345, which reacted intramolecularly with the nucleophilic carboxyl group to furnish a separable anomeric mixture of 5,1-lyxuronic acid
lactone 346.
A general method for the synthesis of γ-acyl-δ-lactones has been developed by
Lugan et al. by vicinal di-functionalization of α,β-unsaturated ketones via manganese carbene intermediates [125] (Scheme 78). Treatment of manganese carbene
347 with n-BuLi generated the carbene anion, which underwent Michael addition
with benzylidene acetone and chalcone to give carbene-enolate intermediate 349. A
cascade aldolization/transesterification of this intermediate with benzaldehyde
afforded the oxacyclocarbene complexes 350, which were readily oxidized by air
to release γ-acyl-δ-lactone 351.
Scheme 77 Synthesis of alduronic acid lactones
Scheme 78 Synthesis of γ-acyl-δ-lactones
Synthesis of Saturated Six-Membered Ring Lactones
135