Dicobalt benzocycloheptyne fused ring via RCM

1. Dicobalt benzocycloheptyne fused ring via RCM Prepared by :Sheida Amiralaei Supervisor: Dr.Green University of Winsor 2005

2. Cycloheptyne benzene fused ring via RCM (A) (B) A wide variety of natural products particulary of the terpene classes possess a fused 7,6-ring system These products can be subjected to transformations for example Pauson –khand reaction or reduction to give cycloheptene

3. Hexacarbonyldicobalt alkyne complexes • Enable the facile formation and trapping of cations in the propargylic position (the Nicholas reaction) • **The cations may be generated from hexacarbonyldicobalt complexes of proprgylic alocohols,ethers,or acetates using either protic or Lewis acids • CHEM. COMMUN., 2002, 1550–1551

4. Hexacarbonyldicobalt alkyne complexes • The ability of the group to participate in novel cycloaddition reactions • Allow bond geometries not available to the metal free alkyne function • Pauson_khand Reaction Is the formal three component [2+2+2] cycloaddition in which cyclopentenones are generated

6. Aromaticity Studying the stability of the cation and aromaticity *1H chemical shiftsareperhaps the most often used criteria for characterizing aromaticity and antiaromaticity. *Li+ chemical shifts and those of the isoelectronic 3He atom are being employed asuseful ringcurrent probes Lithium cations typically complex to the π faces of aromatic systems and the Li+ resonance is shifted upfield due to ring current effect In antiaromatic compounds, however, the Li+ resonance is downfield shifted due to paramagnetic ring current effects, Pure & Appl. Chem., Vol. 68, No. 2, pp. 209-218, 1996

7. Synthesis Of (A) 65%

8. 65% The overall yeild :15%

9. RCM *Longer reaction time and heating of the reaction with Grubbs(I) and Grubb(II) catalysts (using 5% cat) didn’t close the ring

10. RCM • Like other cyclizations that produce medium size ring (seven,eight,nine member) rings, RCM tends to work best when there are conformational constraints that favor ring formation. • Such structural features include the presence of another ring, a gem-dimethyl group, or a N-tosyl group in the chain linking the reacting double bonds.[1] • That a benzene ring constitutes an excellent conformational constraint is illustrated by the use of RCM in recent syntheses of some natural products containing medium-sized oxacycles fused to a benzene ring. Chemical Reviews, 2004, Vol. 104, No. 5

11. Synthesis of (B) (B) (A) So many by products ,low yeild at different conditions

12. 80% 15%

13. 60%