Carbanions II Carbanions as nucleophiles in S N 2 reactions with alkyl halides. a) Malonate synthesis of carboxylic acids b) Acetoacetate synthesis of ketones c) 2-oxazoline synthesis of esters/carboxylic acids d) Organoborane synthesis of acids/ketones
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Carbanions as nucleophiles in SN2 reactions with alkyl halides.
a) Malonate synthesis of carboxylic acids
b) Acetoacetate synthesis of ketones
c) 2-oxazoline synthesis of esters/carboxylic acids
d) Organoborane synthesis of acids/ketones
e) Enamine synthesis of aldehydes/ketones
Start with diethyl malonate and methyl bromide and n-propyl bromide.
Start with ethyl acetoacetate and methyl bromide and n-propyl bromide.
Enzyme = ‘fatty acid synthase”
Condensing Enzyme (CE)
Acyl Carrier Protein (ACP)
step 1) malonyl CoA and acetyl CoA transfer the acetyl and malonate to the carrier enzyme (CE) and acyl carrier protein (ACP) respectively.
step 2) enolate carbanion from malonate (ACP) nucleophilic acyl substitution on the acetyl (CE) followed by decarboxylation.
step 3) reduction of the ketone to a hydrocarbon.
step 4) transfer of the carboxylate from CE ACP to CE.
step 5) malonyl CoA transfers malonate to the carrier enzyme.
step 6) enolate from malonate…etc.
Biological synthesis of fatty acids is analogous to the malonate synthesis of carboxylic acids. The enolate carbanion from malonate acts as a nucleophile in a nucleophilic substitution on the acetyl-CE followed by decarboxylation. Each series puts the three carbon malonate on the ACP and then decarboxylates the substitution product resulting in lengthening the carbon chain by two carbons at a time. Naturally occuring fatty acids are even numbered carboxylic acids.