NOVEL MONOMER FOR PHOTORESIST, COPOLYMER THEREOF AND PHOTORESIST COMPOSITION CONTAINING THE COPOLYMER

2,3-Dihydrobenzofuran derivatives represented by general formula (1), optically active isomers thereof, or pharmacologically acceptable salts of these, wherein R 1 represents hydrogen or acyl; R 2, R 3, and R 4 each represents hydrogen, lower alkyl, or lower alkenyl; and R 5 and R 6 each represents hydrogen or optionally substituted alkyl, or R 5 and R 6 in combination represent cycloalkyl or a saturated heterocycle containing one or more oxygen atoms or alkyl-substituted nitrogen; provided that not both of R 2 and R 3 are t-butyl. The compounds are useful as remedial or preventive agents for various kidney diseases and as organ preservatives.