Stereoselective construction of 3a-methylhydrindanes starting from 2,7-enynol derivatives based on Ti(II)-mediated cyclization and Ru-catalyzed ring-closing metathesis

Low-valent dialkoxytitanium(ii): a useful tool for the synthesis of functionalized seven-membered ring compounds

Herein, we describe unprecedented access to all-carbon or heterocyclic seven-membered ring frameworks from 1,8-ene-ynes promoted by inexpensive low-valent titanium(ii) species, readily available from Ti(OiPr)₄ and Grignard reagent. A broad range of cycloheptane, azepane or oxepane derivatives has been obtained (19 examples) with moderate to good yields and an excellent selectivity (up to 95/5 d.r.).

Synthesis and vitamin D receptor affinity of 16-oxa vitamin D3 analogues

Two novel 16-oxa-vitamin D₃ analogues were synthesized using a tandem Ti(ii)-mediated enyne cyclization/Cu-catalyzed allylation, Ru-catalyzed ring-closing metathesis reaction, and a low-valent titanium (LVT)-mediated stereoselective radical reduction of 8α,14α-epoxide as the key steps for the synthesis of the 16-oxa-C,D ring unit. The vitamin D receptor-binding affinity of the synthesized analogues, 16-oxa-1α,25-(OH)₂VD₃ and 16-oxa-19-nor-1α,25-(OH)₂VD₃, was evaluated by fluorescence polarization vitamin D receptor competitor assay and time-resolved fluorescence energy transfer vitamin D receptor co-activator assay.