[reaction: see text] A new versatile methodology, resulting in a formal three-carbon ring expansion of cyclopentanones, for the efficient assembly of functionalized cyclooctanoids is described. The approach is based on the chemo-, regio-, and stereoselective alpha,gamma-difunctionalization of beta-ketoesters followed by ring-closing metathesis to form functionalized bicyclo[4.2.1]nonanes, precursors of the corresponding cyclooctanes, by selective ring cleavage of the one-carbon-atom bridge.
A series of cis-α,γ-difunctionalized five-membered cyclic β-oxo esters have been chemo-, regio-and diastereoselectively prepared through an efficient domino anionic ring-cleavage/ ring-reconstitution/alkylation sequence including a 1,3-shift of the ester group. These unsaturated substrates were successfully engaged in various ring-closing metatheses to pro-
Rings with 7 or more members Q 0050Stereoselective Synthesis of Bicyclo[4.2.1]nonanes -A Temporary-Bridge Approach to Cyclooctanoids. -An efficient anionic ring cleavage-recyclization--diastereoselective alkylation sequence is presented for the regio-and stereoselective synthesis of 1,3-cis-dienes, e.g. (V) and (IX), or 1,3-cis-enynes, e.g. (XIII). These dienes and enynes undergo ring closing metathesis in the presence of Grubbs' second generation catalyst to give highly functionalized carbonyl-bridged cyclooctene derivatives in most cases. -(MICHAUT, A.; MIRANDA-GARCIA, S.; MENENDEZ, J. C.; COQUEREL, Y.; RODRIGUEZ*, J.; Eur.
The title methology combines a stereoselective anionic domino α,γ-difunctionalization of β-ketoesters with ring-closing metathesis resulting in a formal three-carbon ring expansion. Direct retro-Dieckmann cleavage of bridged ketone (IIa) to liberate the corresponding fused eight-membered is carried out producing a 1:1 mixture of the diastereomers. Product (XI) is successfully transformed to the corresponding monotosylate precursor for a stereoselective Grob-type fragmentation. On reaction with KHMDS in THF, aldehyde (XII) is produced diastereoselectively in 45% yield. -(MICHAUT, A.; MIRANDA-GARCIA, S.; MENENDEZ, J. C.; RODRIGUEZ*, J.; Org. Lett. 6 (2004) 18, 3075-3078; React. Synth. Org., Cent. St. Jerome, Univ. Paul Cezanne, F-13397 Marseille, Fr.; Eng.) -Steudel 50-048
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.