KOH-catalyzed ring-opening

Kress, J. D. Leung, P. G. Tawa, G. J. Hay, P. J. Calculation of a Reaction Path for KOH-Catalyzed Ring-Opening Polymerization of Cyclic Siloxanes. In Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. AGS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 81—97. 

Figure 2. Structures of critical points along the reaction path for KOH catalyzed ring-opening polymerization of D4. TS. Transition state. IP. Insertion product. ROP. Ring-opened product. H atoms on methyl groups are omitted for clarity. C atoms behind the plane of the paper are hidden by out-of-plane C atoms in R and AC.

Figure 3. The gas-phase reaction path of KOH catalyzed ring-opening polymerization of D4 (solid line) and D3 (dash-dot line) calculated with the HF method and 3-21G basis set. The structures along the reaction coordinate for D4 are defined in Figs. 1 and 2. The addition complex (AC) is defined as the zero of energy for both cases. The reaction coordinate is not to scale and is only representative. (Adapted from. ref. 13.)...

Treatment of MFA (1) with cyanogen bromide [6] opened ring G to yield the bromo derivative 3 [7]. Attempts to dehydrobrominate 3 in one step via a base-catalyzed elimination with DBU/CH3CN, KOH/MeOH, or terr-BuOK/DMSO were unsuccessful. However, the required methylene entity could be introduced by converting 3 first to a selenide, then oxidation with periodate, followed by thermolysis in benzene to provide compound 4. Hydrolysis of the cyano group with NaOH in ethylene glycol [8] produced 5 (50% yield). Osmium catalyzed oxidation of 5 in the presence of 4-methylmorpholine A-oxide (NMO) gave a diol, which was cleaved to an aldehyde upon treatment with periodate. Treatment of the aldehyde with sodium cyanoborohydride resulted in an intramolecular reductive animation to yield the desired product PHB (6). 

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