Total Synthesis of Palodesangren B Trimethyl Ether and D Dimethyl Ether via a Late-Stage Formation of 2-Pyran-2-one of the Tetrahydrobenzo[]pyranochromenone Core.

In four steps from the tricyclic core, palodesangren B trimethyl ether and palodesangren D dimethyl ether could be synthesized in 29 and 18% overall yields, respectively. A reaction sequence comprising the regioselective MgCl-mediated Casnati-Skattebøl -formylation of phenol, Wittig methylenation, acryloylation, and Ru(II)-catalyzed ring-closing metathesis (RCM) led to the formation of the final 2-pyran-2-one ring of the desired tetracyclic core.

Divergent Strategy for the Diastereoselective Synthesis of the Tricyclic 6,7-Diaryltetrahydro-6H-benzo[c]chromene Core via Pt(IV)-Catalyzed Cycloaddition of o-Quinone Methides and Olefin Ring-Closing Metathesis.

A divergent strategy for the synthesis of the tricyclic 6,7-diaryltetrahydro-6H-benzo[c]chromene core was successfully developed. The 2,3-trans, 2,4-cis trisubstituted chroman moiety was formed via highly efficient and stereoselective Pt(IV)-catalyzed cycloaddition reactions of the corresponding quinone methides with chalcones. Subsequent steps provided the common diene alcohol, which underwent BF·EtO-mediated EtSiH reduction and olefin ring-closing metathesis (RCM) using Ru(II) catalysts.

Synthesis of C4 - C5 cycloalkyl-fused and C6-modified chromans via ortho-quinone methides.

Starting from 3,5-dimethoxybenzaldehyde, some functionalized 2,3,4-trisubstituted tricyclic 4,5-cycloalkyl-fused and 6-modified chromans could be prepared via ortho-quinone methides (o-QMs)/hetero-Diels-Alder (HDA) reactions of the appropriate precursors. The bromide at C6 served as a handle for introducing other substituents through palladium-catalyzed cross-coupling reactions and other functional-group transformations. Moderate to high yields (up to 80%) and diastereoselectivities (up to >99:1) could be obtained under [PtCl4 ] catalysis.