Lecture32outline

Lecture32outline - • Heterocycles are cyclic molecules...

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I. Review • Reductive amination is an amine preparation in which an aldehyde and an amine react under acidic conditions to form equilibrium concentrations of iminium ions that react selectively with the mild reducing agent NaH 3 BCN (sodium cyanoborohydride) to form amines • The Strecker synthesis is an analog of reductive amination in which an aldehyde and an amine form an iminium ion that reacts with cyanide to form an amino nitrile • The Mannich reaction is similar to the Strecker reaction in that it uses iminium ions as electrophile, but enols are used as nucleophiles to provide carbon-carbon bond formation • Products from the Mannich reaction do not undergo elimination due to the poor leaving group ability of amines • Amines can be alkylated to form quaternary ammonium ions to improve their leaving group ability • Treatment of quaternary ammonium ions with Ag 2 O results in an elimination reaction (Hoffmann elimination)
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Unformatted text preview: • Heterocycles are cyclic molecules that contain a non-carbon atom in the ring • These structures are extremely common in nature, medicine, and the lab, and perform a wide range of functions • Five membered ring aromatic heterocycles can be considered as cyclodehydrated 1,4-dicarbonyl compounds, with hidden enol or enamine equivalents in the structure • Furans can be prepared by exposing 1,4-dicarbonyl compounds to acid and removing water • Pyrroles can be prepared by condensing a 1,4-dicarbonyl compund with a primary amine through a mechanism that follows the mechanism for enamine synthesis II. More heterocycles • Synthesis and reactivity of aromatic five membered ring heterocycles • Synthesis and reactivity of aromatic six membered ring heterocycles Problem Set 25-2, 25-3, 25-9, 25-10, 25-11, 25-13, 25-17, 25-18, 25-20, 25-21, 25-24, 25-25, 25-29, 25-31, 25-32, 25-36, 25-37, 25-46, 25-51...
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