2,3-Dihydrobenzofuran derivatives of general formula (1): wherein R1 represents a hydrogen atom or an acyl group; R2, R3 and R4 represent a hydrogen atom, a lower alkyl group or a lower alkenyl group; R5 and R6 represent a hydrogen atom or an optionally substituted alkyl group, or R5 and R6 combine to form a cycloalkyl group or a saturated heterocyclic group containing one or more oxygen atoms or alkyl-substituted nitrogen atoms, provided that R2 and R3 can not simultaneously represent a t-butyl group, or optically active isomers or pharmaceutically acceptable salts thereof are useful as therapeutic or prophylactic agents for various renal diseases and as organ preservatives.