A concise synthesis of 3,4-fused spiro[isobenzofuran-3-ones], spiro[furo[3,4-b]pyridin-5(7H)-ones], 3-aryl-, and alkylphthalides

Abstract

A synthetically useful protocol has been developed for the preparation of highly functionalized 3,4-fused spiro[isobenzofuran-3-ones], spiro[furo[3,4-b]pyridin-5(7H)-ones], 3-aryl-, and alkylphthalides. Reaction of 2-iodobenzoate esters and 2-iodopyridine carboxylate esters with i-PrMgCl·LiCl in the presence of cyclic ketones under standard Barbier reaction conditions affords 3,4-fused spiro[isobenzofuran-3-ones] and spiro[furo[3,4-b]pyridin-5(7H)-ones] in good to excellent yields. Step-wise addition of i-PrMgCl·LiCl to 2-iodobenzoate esters followed by trapping with various aldehydes yields 3-aryl and 3-alkylphthalides; whereas, under similar conditions access to 3-aryl and 3-alylazaphthalides is also possible. Extension of this methodology toward the preparation of 3-n-butylphthalide and chrycolide, a natural product isolated from the leaves and stems of Chrysanthemum coronarium, is also described.