Synthesis of Dibenzocyclooctyne-Dicobalt Hexacarbonyl and Dibenzocycloheptyne-Dicobalt Hexacarbonyl Complexes by Intramolecular Nicholas Reactions: Synthesis of Isoschizandrin, Schizandrin A and Tenuifolin

Biaryl propargyl acetate dicobalt hexacarbonyl complexes readily undergo Lewis acid mediated intramolecular Nicholas reactions to afford dibenzocycloheptyne complexes. This thesis describes the extension of this protocol towards studies of intramolecular Nicholas reactions with similar biaryl complexes to form dibenzocyclooctyne–Co2(CO) 6 complexes. These investigations have been performed on several different derivatives of biaryl systems and have afforded fair to good yields of dibenzocyclooctyne–Co 2(CO)6 complexes. One of the major factors governing the yield of intramolecular Nicholas reactions was found to be the amount of Lewis acid employed along with absence or presence of EtNiPr 2. The studies conducted have also shown that in some cases, upon the cyclization there is restriction of the biaryl axial rotation due to the four ortho substituents, which constitutes formation of an axis of chirality. In addition, we have also exploited intramolecular Nicholas reactions of biaryl propargyl acetate dicobalt hexacarbonyl complexes towards the synthesis of tenuifolin.