Toward a Total Synthesis of Macrocyclic Jatrophane Diterpenes – Concise Route to a Highly Functionalized Cyclopentane Key Intermediate

A total synthesis of the biologically potent jatrophane diterpenes pepluanin A ( 1 ) and euphosalicin A ( 2 ) is being aimed at. En route to these targets, a concise synthesis of the nonracemic cyclopentane building block 74 was developed. Key steps were a Claisen–Eschenmoser rearrangement of the enantiomerically enriched allylic alcohol 14 to amide 34 ( Scheme 7 ), a hydroxy‐lactonization of 40 to 43 ( Scheme 9 ), followed by trans ‐lactonization to 72 , which was subjected to a Davis hydroxylation to 69 ( Scheme 17 ). Eventually, compound 69 was converted into the enol triflate 74 . This material should prove suitable for an annulation of the macrocyclic ring characteristic of the desired jatrophanes 1 and 2 . Less‐successful approaches are also discussed due to their intrinsically valuable information content.