Abstract: Intermediates for the preparation of himbacine exhibiting muscarinic M2 receptor antagonism, which are hydronaphtho[2,3-c]furan derivatives represented by general formula (1) or intermediates for the preparation thereof: wherein R1 is lower alkyl or aralky; R2 is hydrogen, lower alkyl or aralkyl; R3 and R4 together represent oxygen or methylene, or alternatively R4 is hydroxyl, lower alkoxy, aralkyloxy or lower acyloxy, with R3 being hydrogen; R5 and R6 together represent oxygen, or alternatively R6 is hydroxyl, lower alkxy, aralkyloxy or lower acyloxy, with R5 being hydrogen; and either of the broken lines is a single bond and the other thereof is a double bond, or alternatively both are single bonds.