2-Cyclopenten-l-ones

It has been recently reported that the reactions of 1,4-dilithio-l,3 dienes with carbon monoxide provides a useful tandem methodology for the synthesis of cyclopentenones14. The reaction constitutes an unprecedented pattern of highly selective efficient carbonylation, since in 1 h at — 78 °C it affords, after hydrolysis, fraws-3-cyclopenten-l-one in an excellent isolated yield and with perfect trans selectivity. 

The reaction of 1,4-dilithio-l,3-dienes with CO mentioned in Section n.A constitutes a useful methodology for the tandem synthesis of substituted 3-cyclopenten-l-ones with perfect trans selectivity (Scheme 5)105. Carbolithiation of unsaturated C—C bonds is a... 

Cycloadditions. 1,2,4-Trienes participate in cycloaddition, using their conjugated diene moieties, with alkynes and carbon monoxide to give aromatic products and 2-alkylidene-3-cyclopenten-l-ones, respectively. The latter process is subject to asymmetric induction of chiral phosphine ligands. 

Still another possibility of isomerization is illustrated by the easy interconversions between pentaphenylpentadienoic acid chloride and 2-chloropentaphenyl-3-cyclopenten-l-one. Interestingly, 2,4,6-trimethylpyrylium iodide may be sublimed without decomposition in a vacuum, possibly as a covalent 6-iodo-4-methyl-3,5-heptadien-2-one or 2-iodo-2,4,6-trimethyl-2if-pyTan valence isomer. In a related case, ohlorocyclopropenes are covalent and are converted into cyclo-propenium derivatives only by the action of Friedel-Crafts catalysts (electron-deficient metallic chlorides) (cf. also Section II,C,2,c.)... 

Cyclobutanone and 3-Cyclopenten-l-one in the first singlet excited states. 

As a test for checking the eflfectiveness of the model, we have applied the procedure and determined the optimal geometries of two relatively large molecules cyclobutanone and 3-cyclopenten-l-one 16], which are well known in their first (n — ir ) excited state (23-26]. 

In the same way, 3-cyclopenten-l-one was considered in both the singlet fundamental and the first (n — tt ) excited states. The geometries were also optimized at RHF and HPHF levels, respectively, using the same basis set [28. ... 

The reaction of di-hthio reagents 1 with CO at —78°C for 1 h afforded trans-3-cyclopenten-l-one 30 in an excellent isolated yield and with trans selectivity after hydrolysis (Scheme 14) [59]. Deuteriolysis of the reaction mixture afforded dideuterated products with more than 98% of deuterium incorporation. This reaction featured high efficiency and regio- and stereoselectivity, which showed an tmprecedented pattern of highly selective and efficient carbonylation of organolithium reagents. 

Song Q, Chen J, Jin X, Xi Z (2001) Highly regio- and stereoselective 1,1-cycloaddition of carbon monoxide with 1,4-dilithio-l,3-dienes. Novel synthetic methods for 3-cyclopenten-l-one derivatives. J Am Chem Soc 123 10419-10420... 

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