Membered Rings Fuchs

For reviews of the conformational analysis of five-membered rings, see Fuchs, B. Top. 

Recent synthetic applications of the photochemical [2 -I- 2] cycloaddition of unsaturated sulfones have been noted. Musser and Fuchs have effected an intramolecular [2 -I- 2] addition of a 6-membered ring vinyl sulfone and a five-membered ring vinylogous ester in excellent yield, as part of a synthetic approach to the synthesis of the mould metabolite, cytochalasin C. The stereospecificity of the addition was only moderate, however, and later problems with this synthetic approach led to its abandonment. Williams and coworkers have used the facile [2 + 2] photoaddition of 73 and... 

For reviews of the conformational analysis of five-membered rings, see Fuchs Top. Stereochem. 1978, 70, 1-94 Legon. Ref. 251 -... 

Fuchs has used this reaction type for the construction of an 11-membered ring in the course of model studies for the [ll]cytochalasin synthesis. These cytostatic compounds, e.g. cytochalasin C (109), are metabolites of microorganisms. Reductive fragmentation of the benzenesulfonates (110 Scheme 37) produces the dienols (111). In contrast, both the sulfonates (112) on treatment with LDA afford the tricyclic ketones (113), the products of internal alkylation. Less than 1% of (111) is formed. In conclusion, the author points out that the enolate conformation (Scheme 37, in parentheses) appears to be all important in determining the reaction products of the four diastereoisomers (110) and (112). Whenever the enolate can easily assume a folded conformation, the tricyclic cyclobutane (113) will result. Models of the enolates of (110), where the intraannular fragmentation successfully occurs, show that the folded conformations are more strained than are the extended conformations. 

Fig. 7 Snapshots showing the pulling of a thiolate molecule from a gold substrate. The darker gold atoms indicate the atoms which are fixed and the arrow indicates the direction in which the terminal carbon atom is moved. After extraction of a three atom gold wire, an isomerisation reaction occurs to form a three membered gold ring. Reprinted with permission from D. Kruger, H. Fuchs, R. Rousseau, D. Marx and M. Parrinello, Phys. Rev. Lett., 2002,89,186402. Copyright 2002 by the American Physical Society.

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