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480 Organic Chemistry Solutions Manual Problem 7 This rearrangement was studied as a biomimetic version of the NIH shift. Write a mechanism for the reaction. Do you consider it a good model reaction? If not, how might it be made better? CO₂Me OH CO₂Me 0 pH 7 CO₂Me Purj 83% yield 17% yield and Purpose of the problem Exploration of an enzymic mechanism by model reactions. The Suggested solution The epoxide opens to give mainly a cation stabilized by the alkenes but not conjugated to the labell destabilizing ester group. The group then migrates. The minor product comes from opening the epoxide the other way round. The methyl group at the bottom of the ring is important as a of lb: marker to show definitely that the CO₂Et group has migrated. H MeO₂C OH 0 CO₂Me 0 H CO₂Me + H MeO₂C CO₂Me H oH CO₂Me Re This is quite a good model reaction in that it shows that monoepoxides of benzenes can undergo a rearrangement quite like the NIH shift (pp. 1407-10) but in the real thing a hydrogen atom migrates with its electrons rather than the very different CO₂Et group. However, it is very difficult to make epoxides of aromatic rings without some substituent other than hydrogen and this is one (2) limitation of model studies. Problem 8 The following experiments relate to the chemical and biological behaviour of NADH. Explain what they tell us. (a) This FAD analogue can be reduced in vitro with NADH in D₂O with deuterium incorporation in the product as shown. Me Me D N N 0 N N NADH NMe D₂O NMe H 0 H H