A direct synthesis of α-methylene ketones

Asymmetric Total Synthesis of (−)‐Nakadomarin A

“…After the primary alcohol was protected as a TBDPS ether, the N ‐benzenesulfonyl group in ring A was selectively removed with sodium anthracenide to give 11 , which was then converted into unsaturated aldehyde 12 by contraction of ring B. The six‐membered ring B was cleaved by ozonolysis to give an unstable bisaldehyde, which was recyclized to a five‐membered ring by aldol condensation with N ‐methylanilinium trifluoroacetate 9. Wittig reaction of aldehyde 12 selectively gave Z olefin 13 , which was quantitatively converted into endoperoxides 14 as a mixture of two diastereomers ( 14 a / 14 b =1.2:1) by singlet oxygen.…”

Probing the mechanism of direct Mannich‐type α‐methylenation of ketoesters via electrospray ionization mass spectrometry

“…α,β‐Unsaturated carbonyl compounds are of great importance in organic synthesis. One of their most pronounced characteristics is high reactivity towards various nucleophiles1–6 in reactions that can form two or more chiral centers. These versatile reagents are also used as building blocks in many asymmetric transformations, including Diels‐Alder cycloadditions,7–9 Michael addition,10 1,3‐dipolar cycloaddition reactions11, 12 and bioreductions 13–18.…”

Highly Enantioselective Construction of Fused Pyrrolidine Systems That Contain a Quaternary Stereocenter: Concise Formal Synthesis of (+)‐Conessine

“…Starting from commercially available 6‐methoxy‐1‐tetralone ( 12 ), the enyne 15 was readily prepared (Scheme ). A direct methylene‐transfer reaction by a general synthetic method produced the α‐methylene enone 13 from 12 8. The Michael addition of ( R )‐(+)‐ N ‐methyl‐ N ‐(1‐methyl‐2‐propynyl)amine ( 3 ) to the enone 13 catalyzed by activated alumina9 gave the adduct 14 in 95 % yield.…”