Science of Synthesis

Marsden, S. P., Science of Synthesis, (2005) 26, 1066.

Direct halogenation adjacent to a ketone followed by base-mediated elimination is a simple route to enones. Halogenation can be achieved under a variety of conditions such as direct treatment with bromine,[‌95‌,‌96‌] bromine in the presence of acetic acid,[‌97‌] N-bromosuccinimide,[‌98‌] or, for chlorides, sulfuryl chloride.[‌99‌] Elimination is usually mediated by an amine or an inorganic base such as calcium carbonate. In carbonyl compounds with only one site for enolization such as ‌99‌ the reactions are simple (‌Scheme 25‌),[‌95‌,‌97‌] but in substrates with more than one site for enolization the possibility of regioisomers must be considered. Direct treatment with bromine usually gives the more substituted bromide and hence an α-substituted enone.[‌96‌] Treatment of α-substituted cyclopentanones such as ‌100‌ with N-bromosuccinimide followed by aniline-mediated elimination gives the more substituted product (e.g., ‌101‌) but apparently through initial bromination at the less substituted position followed by alkene migration.[‌98‌] A convenient regiospecific approach to α-unsubstituted enones is demonstrated in the construction of enone ‌103‌. Bromination of β-oxo ester ‌102‌ is followed by elimination carried out under conditions where Krapcho decarboxylation also occurs, yielding ‌103‌ directly.[‌100‌]

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8-Meeeeeeeeeeeeee-8-eeeee (‌888‌); Meeeeee Meeeeeeee:[‌88‌]

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References

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• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) 8/8e, 8888.
• 8.Meeeee-Meee, (8888) M 88e8, 888.
• 8.Meeeee-Meee, (8888) M 88e8, 88.