Type of Document Thesis Author Song, Euhno URN etd-05062005-172529 Title Ring-Closing Metathesis for the Synthesis of Carbocyclic and Heterocyclic Intramolecular Baylis-Hillman Adducts Degree Master of Science Department Chemistry and Biochemistry, Department of Advisory Committee
Advisor Name Title MARIE E. KRAFFT Committee Chair ARMEN ZAKARIAN Committee Member GREGORY B. DUDLEY Committee Member JOSEPH B. SCHLENOFF Committee Member Keywords
- INTRAMOLECULAR BAYLIS-HILLMAN
Date of Defense 2005-04-26 Availability unrestricted AbstractWe have investigated optimum conditions for the Baylis-Hillman and ring-closing metathesis (RCM) reactions. In our experiments, we obtained the best results with quinuclidine (0.25 eq), and MeOH (0.75 eq) for the Baylis-Hillman reaction and 10 mol % of Grubbs #2 with DCM (0.01 M) for the RCM.
We performed further reactions based on these optimum conditions. We examined the Baylis-Hillman and RCM reactions the under same conditions in order to extend the ring size from 5-membered to 8-membered and succeeded in the generation of 5-, 6- and 7-membered ring RCM products in 46 %, 67 % and 66 % yields. In the case of longer chains, only cross metathesis products (dimerized products) were detected after the reaction time.
From these results, we focused our attention on the construction of 5- or 6-membered cyclic frameworks. At first, we applied optimum conditions for construction of 5-membered rings with a- or a,b-substituted aldehydes. Unfortunately, our attempts to form 5-membered rings with a-substituted aldehydes did not proceed well in the RCM due to steric hindrance. Interestingly, the nitrile-substituted 5-membered ring was readily formed in the RCM in good yield.
Second, we performed the synthesis of ring-fused RCM products from Baylis-Hillman adducts using three different aldehydes. The experimental results were shown that only the Baylis-Hillman adduct from benzaldehyde gave a good yield (92 %) in the RCM reaction.
Third, we achieved the synthesis of 6-membered carbocyclic RCM products from BH adducts using b-substituted hexenal. We employed 3-methyl and 3,3-dimethyl-5-hexenal in the BH reaction and ultimately obtained desired RCM products in same yield (87 %). It means that steric effects from substituents on the b-position of aldehydes is a not predominant factor influencing the reaction yield.
In the end, 6-membered heterocyclic RCM products from BH adducts using chiral amino acids were completed through several well-known steps. These applications have been developed for a combinatorial approach for the construction of heterocyclic frameworks.
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