Organocatalytic [4+4] annulation of indole-4-boronic acid with o-hydroxybenzyl alcohols for constructing indole-fused oxaborocanes

An organocatalytic [4+4] annulation between indole-4-boronic acids and o -hydroxybenzyl alcohols has been developed. This method enables the synthesis of a diverse range of indole-fused oxaborocanes in generally good yields. Moreover, by employing a chiral phosphoric acid catalyst, the corresponding chiral indole-fused oxaborocanes were obtained with high enantioselectivity. This work not only reports the first synthesis of indole-fused oxaborocanes and achieves their enantioselective preparation, but also demonstrates the first use of indole-4-boronic acids as four-atom synthons in annulation reactions. Furthermore, this study offers a novel strategy for constructing chiral indole-fused boron-containing eight-membered rings, thereby contributing valuable insights to the fields of chiral indole chemistry and boron chemistry. An organocatalytic [4+4] annulation between indole-4-boronic acids and o -hydroxybenzyl alcohols has been developed to access indole-fused oxaborocanes with high efficiency. This work not only reports the first synthesis of indole-fused oxaborocanes and achieves their enantioselective preparation, but also demonstrates the first use of indole-4-boronic acids as four-atom synthons in annulation reactions.