Studies on Agarofurans Ⅲ. The Synthesis of 3-Substituted Agarofurans

14-Nor-3-oxodihydroagarofuran (2) was prepared in high yield. From 2, derivatives12 and 13 were synthesized by Grignard addition. In order to identify the configuration of C-3 in compound 12 and 13, the sterospecific synthesis of compound 12 has been carried out in 5 steps from octalone (14).