The first total syntheses of (+/-)-didehydrostemofoline (1) and (+/-)-isodidehydrostemofoline (3) are reported. The synthesis begins with the Diels-Alder reaction of readily available pyrrole 9 and ethyl (E)-3-nitroacrylate, the latter serving as a regioinverted equivalent of ketene. After hydrogenation to prevent retro-Diels-Alder reaction, the major cycloadduct is transformed to 7-azabicyclo[2.2.1]heptanol 14. Aza-Cope-Mannich reaction of the formaldiminium derivative of 14 delivers 1-azatricyclo[5.3.0.04.10]decane 15, which in 15 additional steps is converted to 1 and 3.
The antineoplastic agent (−)‐metachromin A (1) from Hippospongia metachromia has been synthesized in enantiomerically pure form in 13% overall yield. A general convergent synthetic strategy for different metachromins using a 2‐alkyloxy‐3‐sulfonyl‐1,3‐oxazolidine as a chiral dithienium equivalent is presented.
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