Synthesis of Okaramine M, Its Conversion to Amauromines, and Concise Bidirectional and Biomimetic Total Synthesis of Amauromines

A synthesis of exo- and endo-okaramine M and their conversion into different sets of stereoisomers of amauromines are reported. Moreover, a short bidirectional and biomimetic total synthesis of amauromines is described using an Ir-catalyzed double prenylation as the key step. Accordingly, amauromine with its six stereogenic centers can be prepared in two synthetic steps in enantiomerically pure form starting from unprotected l-tryptophan.