A Concise Route to Branched Erythrono-γ-lactones. Synthesis of the Leaf-Closing Substance Potassium (±)-(2<i>R</i>,3<i>R</i>)-2,3,4-Trihydroxy-2-methylbutanoate

A series of 1,2-dioxanes 3 were ring-opened with Co(SALEN)2 to furnish lactol regioisomers 4 and 5 (86−99% yield). The lactols were oxidized to γ-lactones 8 and 9 (72−96% yield) and deprotected to afford the 2-C- and 3-C-alkyl and aryl branched erythrono-γ-lactones 1, 6, and 7 (65−94% yield), including the natural plant lactone (±)-2-C-d-methylerythrono-1,4-lactone 1. The latter compound was treated with aqueous potassium hydroxide to afford potassium (±)-(2R,3R)-2,3,4-trihydroxy-2-methylbutanoate 2, which is a leaf-closing substance of Leucaena leucocephalam.