Ketones, cyclic, conjugated alkenes

Compound A is a cyclic, nonconjugated keto alkene whose carbonyl infrared absorption should occur at 1715 cm-. Compound B is an a,B-unsaturated, cyclic ketone additional conjugation with the phenyl ring should lower its IR absorption below 1685 cm-1. Because the actual IR absorption occurs at 1670 cm-1, B is the correct structure. 

Similar reactions have been carried out on acetylene. Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones. In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopen-tanone with a rhodium-complex catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. ... 

In contrast to a, -ethylenic ketones or even a, -ethylenic sulfones, a, ) -ethylenic sulfoxides generally are not sufficiently electrophilic to undergo successful nucleophilic j8-addition . a-Carbonyl-a, j8-ethylenic sulfoxides, however, are potent, doubly activated alkenes which undergo rapid and complete -addition of various types of nucleophiles even at — 78 °C. A brief account summarizing this area is available . The stereochemical outcome of such asymmetric conjugate additions to enantiomerically pure 2-sulfmyl 2-cycloalkenones and 2-sulfinyl-2-alkenolides has been rationalized in terms of a metal-chelated intermediate in which a metal ion locks the -carbonyl sulfoxide into a rigid conformation (36 cf. 33). In this fixed conformation, one diastereoface of the cyclic n... 

A powerful method to convert non-conjugated keto olefins into cyclic alcohols [46,47] utilizes the cathodic reduction of a ketone to afford a ketyl, which subsequently undergoes cyclization onto the pendant alkene. As illustrated in Eqs. (27H30), the process provides access to mono-, bi-, and heterocyclic systems from very simple starting materials. It is especially well-suited to the construction of five-membered rings, less so for six-, and is not effective in producing seven-membered rings. 

One may well ask why the isomerization of alkenes discussed in the preceding section requires a sensitizer. Why cannot the same result be achieved by direct irradiation One reason is that a tt — tt singlet excited state (5,) produced by direct irradiation of an alkene or arene crosses over to the triplet state (Ij) inefficiently (compared to n —> it excitation of ketones). Also, the Si state leads to other reactions beside isomerization which, in the case of 1,2-diphenyl-ethene and other conjugated hydrocarbons, produce cyclic products. For example, cw-l,2-diphenylethene irradiated in the presence of oxygen gives phenanthrene by the sequence of Equation 28-8. The primary photoreaction is cyclization to a dihydrophenanthrene intermediate, 6, which, in the presence of oxygen, is converted to phenanthrene ... 

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