Synthesis of (+)-Myrtopsine, (+)-7,8-Dimethoxymyrtopsine, and Related 2,3-Dihydro-3-hydroxy-2-(1-hydroxy-1-methylethyl)benzofuran Natural Products

The first syntheses of myrtopsine (8t) and 7,8-dimethoxymyrtopsine (9t) have been carried out by halogen-metal exchange of 3-iodo-4-methoxyquinolin-2(1H)-ones ( 15) and ( 21) with i-PrMgCl followed by addition of 3,3dimethyloxirane-2-carboxaldehyde (1).A two-step sequence leads selectively to trans-2,3-dihydro-3-hydroxy-2-(1-hydroxy-1-methylethyl)benzofurans (7t), (8t), ( 9t), ( 28), and ( 32) by conversion of a 2-iodophenol or a 3-iodo-4methoxyquinolin-2(1H)-one to an aryl Grignard reagent and addition of 3-methyl-2-butenal, followed by threo selective epoxidation of the resulting allylic alcohol and cyclization with inversion.