Alkenyl Systems

FIGURE 3.12. (a) Full NMR spectrum of (Z)-l-fluoropentene. (b) Details of NMR spectrum of (Z)-l-fluoropentene 

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Scheme 8.9. Palladium-Catalyzed Alkenylation of Aryl and Alkenyl Systems... 

Another approach to avoiding such metabolic degradation while retaining a smaller and more polar type of R group utilizes an auxiliary compound to separately inhibit the Penicillinase, much as we saw for the case of the earlier levodopa example. For the PENs, the auxiliary compound is clavulanic acid, shovm as 66. When the beta-lactam moiety in 66 is being attacked by the Penicillinases, its unique hydroxymethylene-alkenyl system serves to further alkylate this enzyme in an irreversible manner at some other nucleophile. Hence, the enzyme cannot regenerate itself for a new attack of a beta-lactam system of any type. Thus, coadministration of 66 with a broad- or extended-spectrum PEN derivative is ultimately able to overcome the SAR paradox that is otherwise difficult to achieve within just a single molecule. 

During the development of the Heck reaction of vinylBhg, silver(i) (or thal-lium(i)) acetate was shown to be a useful stoichiometric additive for enhancing the selectivity in favor of the Heck-product, especially when the coupling partner is an alkenyl system. In the latter case, further improvement can be found in replacing triphenylphosphine with tri(o-tolyl)phosphine and using silver(i) acetate as the sole base. ... 

Phenylselenyl nucleoside derivatives have been used as precursors of alkenyl systems, as in the case of the conversion of (125), made from the 2,2 -anhydronucleoside, into (126) on treatment with MCPBA. The same approach was also used to prepare 2 -, 3 - and 4 -enes, although with variable regiocontrol in the eliminations. ... 

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