Lecture33outline

Lecture33outline - I. Review Pyrazoles contain adjacent...

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I. Review • Pyrazoles contain adjacent nitrogen atoms and can be viewed as an imine and an enamine • Pyrazoles are constructed by condensing hydrazine or a monoalkyl hydrazine with a 1,3-dicarbonyl compound • The carbon between the oxygen and nitrogen in oxazoles is at the carboxylic acid oxidation state • The initial step in oxazole synthesis proceeds through the reaction of hydroxy amides with a dehydrating agent such as SOCl 2 • This process proceeds through a Vilsmeier intermediate (chloroiminium ion) that cyclizes by intramolecular hydroxide addition followed by tetrahedral intermediate breakdown to extrude chloride • The resulting product (oxazoline) can be oxidized to form the oxazole with 2,3- dichloro-5,6-dicyanobenzoquinone (DDQ), a benchtop surrogate for NAD + • Fusion of a five-membered ring to a phenyl ring is commonly observed, producing structures such as benzofurans and indoles (very important structures) • These structures can be prepared by condensing phenols or anilines with carbonyl
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Lecture33outline - I. Review Pyrazoles contain adjacent...

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