A nonenzymatic self-assembly program was introduced to explore diverse clavatol-based pseudonatural products (PNPs) in a marine-derived fungus. Intermolecular couplings of the chemoreactive ortho-quinone methide of clavatol with native acceptors led to 14 clavatol-based PNPs with five categories, and compounds 1, 2, 5-10, and 12 are new. In particular, 1 and 2 possessed an unprecedented oxa-angular tetracyclic scaffold with highly oxidized modification and exhibited cytotoxicity. Such a program is proven to be of great advantage in constructing bioactive PNPs.