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The Claisen Ester The Claisen Ester Condensation Condensation • Esters, like aldehydes and ketones, have acidic -hydrogens. • When an ester bearing an -hydrogen is treated with a strong base, a condensation reaction takes place to yield a -ketoester. WWU -- Chemistry WWU -- Chemistry The Claisen Ester The Claisen Ester Condensation Condensation O R CH C O CH CH 2 2 3 O O + NaOCH CH 2 3 R CH C CH C O CH CH 2 2 3 O R R CH C O CH CH 2 2 3 a ketoester + NOTE: The alkoxide should match the CH CH O H alkyl group of the ester in order to avoid 3 2 a competing transesterification. WWU -- Chemistry WWU -- Chemistry Claisen Ester Condensation -- Claisen Ester Condensation -- Mechanism (Part One) Mechanism (Part One) 1) O .. _ CH C OCH O :O: 3 2 5 fast _ + HO CH + :CH C OCH CH C OCH 2 5 2 2 5 2 2 5 _ .. :O C H .. 2 5 enolate ion O acceptor .. _ 2) :O: CH C OCH 3 2 5 CH C OCH slow 3 2 5 O O _ CH C OCH :CH C OCH 2 2 5 2 2 5 donor WWU -- Chemistry WWU -- Chemistry Claisen Ester Condensation -- Claisen Ester Condensation -- Mechanism (Part Two) Mechanism (Part Two) 3) .. _ :O: :O: CH C OCH 3 2 5 fast CH3C O O CH C OCH 2 2 5 CH C OCH 2 2 5 + _ .. :O CH .. 2 5 WWU -- Chemistry WWU -- Chemistry The Key to Claisen Ester The Key to Claisen Ester Condensations Condensations • The -carbon of the donor attaches itself to the carbonyl carbon of the acceptor. • The alkyl group of the acceptor leaves to form a C=O bond. WWU -- Chemistry WWU -- Chemistry
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