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26.9.1.1.15 Method 15: α′-Alkylation of Preformed α,β-Unsaturated Ketones

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261095.

The site of kinetic deprotonation of enones is the α-position, leading to cross-conjugated dienolates. Kinetic deprotonation is usually achieved with strong bases such as lithium amides, and the resulting enolates undergo clean alkylation, leading to α-substituted enones (e.g., conversion of 283 into 284, Scheme 49).[‌229‌] Vinylogous esters such as 143 can also be alkylated in the α-position by similar protocols giving enones, e.g. 285.[‌230‌] Such reactions form part of a protocol for the indirect synthesis of γ-alkylated enones (see Section 26.9.1.1.16.2). 3-Alkoxycyclopent-2-enones such as 286 can undergo a double deprotonation, since the initially formed enolate creates a cyclopentadiene skeleton which undergoes deprotonation to the aromatic cyclopentadienyl anion 287.[‌231‌] The di­anions undergo annulation reactions with double electrophiles, yielding fused bicyclic enones (e.g., 288) in a single operation.

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