Efficient and versatile synthesis of 5-O-acylquinic acids with a direct esterification using a p-methoxybenzyl quinate as a key intermediate

An efficient and versatile synthesis of 5-O-acylquinic acids from commercially available (−)-quinic acid was accomplished. We designed p-methoxybenzyl quinate as a key intermediate, and two problems, the esterification of the sterically hindered 5-OH group for the concise divergent synthesis and the low yield of the final deprotection step, were solved. For the first problem, we improved Tanabe's method, TsCl/NMI-mediated esterification using free carboxylic acids, by the addition of i-Pr2NEt. For the second problem, we established a TFA- or BCl3/C6HMe5-catalyzed deprotection reaction for the final deprotection step. 5-O-Acylquinic acids were synthesized in seven steps with 45–60% overall yield.