Cycloaddition precursor cyclohexadiene

Of course, this was only a theory—until in 1982 K.C. Nicolaou s group synthesized the proposed endiandric acid precursor polyene—and in one step made both endiandric acids D and E, plus endiandric acid A, which arises from a further pericyclic reaction, an intramolecular Diels-Alder cycloaddition of the acyclic diene on to the cyclohexadiene as dienophile. 

The most general synthetic route to benzene oxides-oxepins is that initially developed by Vogel for 1. 1,4-cyclohexadienes (readily available from [2+4] cycloaddition of alkynes and butadienes, lithium-ammonia reduction of arenes, or dehydration of cyclohexenols) were converted to dibromoepoxides, the immediate precursors of benzene oxides. Modifications of this route have been used to prepare Ic and Id. Treatment of the monosubstituted arene oxide 43 (Figure 3) with (Et)4NF or thermal isomerization of 3-oxaquadricyclane provide additional synthetic routes to la. Similarly, the thermal (or photochemical) isomerization of the monoepoxide of Dewar benzene yielded la. ... 

Compared with the reaction with cyclohexadiene, the diastereoselectivity of the Diels-Alder reaction of 122 with cyclopentadiene was found to be lower under a variety of reaction conditions. In the latter case, the cycloaddition afforded the [2.2.1] bicyclic salt 129, which was further converted to 130 — the precursor of a carbocyclic L-nucleoside [95] (Scheme 10.41). 

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