Conjugated ketenes

Ketenes and related compounds have been reviewed extensively (1 9). For the synthesis and synthetic uses of conjugated ketenes see Reference 10. Ketenes with three or more cumulated double bonds have been prepared (11,12). The best known is carbon suboxide [504-64-3] 3 2 preparative uses and has been reviewed (13—16). Thioketenes (17,18), ketenimines (19—21), and their dimers show interesting reactivity, but they have not achieved iadustrial importance to date. 

The second reaction pathway investigated was a o-QM decomposition initiated by a ring-opening process, generating a conjugated ketenes as intermediate, as shown in Scheme 2.18. 

Cazes, B. Julia, S. Preparation and utilization of two C5 conjugated ketene dithioacetals as isoprene synthons. Synthesis of (-)-(E)-lanceol. Tetrahedron Lett. 1978, 4065—4068. 

Rhj(OAc), catalyzes the uansfc and episulfoxides to norbomene am Conjugated ketenes. a-Dtaz... 

Conjugated ketenes. a-Diazo-y.S-unsaturated P-ketoesters undergo rearrangement to ketenes which enter Diels-Alder reactions as dienes toward electron-rich alkenes. Substituted phenols are acquired. 3-Acyloxy-2-chloro-2-cyclohexenones are formed when 2-diazocyclohexane-l,3-diones are treated with acid chlorides in the presence of Rh COAc),. ... 

Balczewski, P., and Mikolajczyk, M., Sulfenylation of tz-phosphoryl sulfides. Chemical evidence for intermediate formation of a-phosphoryl trithioorthoformate, Heteroatom Chem., 5, 487, 1994. Mikolajczyk, M., and Balczewski, P., Org anosulphur compounds. Part 71. Diverse reactivity of a-carhanions derived from a-phosphoryl dithioacetals and a-phosphoryl sulphides towards a.P-unsat-urated carhonyl compounds. A general synthesis of conjugated ketene dithioacetals. Tetrahedron. 48. 8697, 1992. 

Conjugated ketene thioacetals have been successfully prepared starting with aldehyde dimethylhydra-zones. In these reactions, the first-formed azaallyllithium reagent was allowed to react with carbon disulfide to form an intermediate lithium 3-dimethylhydrazonoalkanedithiolate. A second deprotonation of this dithiolate with a second equivalent of LDA then generated a dianion that was successfully alkylated with two equivalents of methyl iodide to yield the ketene thioacetal (e.g. 55 equation 25). This two step sequence avoided competing formation of a methyl dithiocarbamate by addition of LDA to carbon disulfide. 

When a conjugated ketene generated in situ adds to the Er(III) complex of amino alcohol 150, its conformation is fixed. The metal center also attracts an aldehyde to proceed with the hetero-Diels-Alder reaction." ... 

H.W.Moore and O.H.W.Decker, Conjugated Ketenes New Aspects of Their Synthesis and Selected Utility for the Synthesis of Phenols, Hydroquinones and Quinones, Chem.Rev., 1986, 86, 821. 

Conjugated ketenes are derivatives of ketenes, which have some TT-bonds conjugated with the TT-bond in ketene. The conjugating properties modify the electronic structures and the reactivities of conjugated ketenes as compared to other nonconjugated ones. These three kinds of conjugated ketenes ct-oxoketenes, imidoylketenes, and alkenylketenes, and their preparations and cycloaddition reactions will be introduced in this review. 

In 1985 Harold W. Moore and co-workers (University of California, Irvine), described the generation and chemistry of 2-alkenylethynyl ketenes, which were accessible from the corresponding alkynylcyclobutenones. For example, 4-alkynyl-4-trimethylsililoxycyclobutenone 3 forms an enyne-ketene 4. The conjugated ketene 4 undergoes ring closure to produce the diradical 5 (or related zwitterion) which, in turn, proceeds to the substituted... 

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