Development of novel Lewis acid catalyzed cycloisomerizations: synthesis of bicyclo[3.1.0]hexenes and cyclopentenones

A Mechanistic Spectrum of Chemical Reactions

“…Recently, novel cycloisomerizations were found to be catalyzed by Lewis acid and to afford bicyclic products [39] as photochemical reactions do [40]. The new finding supports the mechanistic spectrum of chemical reactions.…”

“…Trauner and colleagues [39] recently found a striking contrast in the thermal and catalyzed reactions of a triene. Thermal reaction of a trienolate readily underwent disrotatory electrocyclization to afford cyclohexadiene (delocalization band in Scheme 8) in accordance with the Woodward-Hoffmann rule.…”

The total synthesis of (–)-crispatene

“…This approach required the cross-coupling of vinyl stannane 35 with the previously obtained vinyl iodide 13. The ␣-methoxy-␥-pyrone building block 35 was obtained from the known iodomethacrylic amide 31 (21) (11). Note that the 6 electrocyclization product of tetraene would form an immediate precursor of tridachiapyrone A (5).…”

“…Although the photochemical biosynthetic origin of the bicyclo[3.1.0]hexene natural products appears to have been established, at least in the case of photodeoxytridachione, we have been intrigued by the possibility that these compounds could also arise from a thermal [ 4 a ϩ 2 a ] cycloaddition involv-ing precursors of type 10a,b (Scheme 1). Recently, we have reported the Lewis acid-catalyzed cycloisomerization of polyenes related to 10a,b to bicyclo[3.1.0]hexenes and the application of this reaction to the total synthesis of racemic photodeoxytridachione (6) (10,11). This reaction could proceed as a [ 4 a ϩ 2 a ] cycloaddition or involve a stepwise mechanism.…”

Mapping the Chemistry of Highly Unsaturated Pyrone Polyketides

“…Provided this last step is considerably faster than rotation around the C2-C3 bond, the reactions could proceed stereospecifically. 12,16 Scheme 11 The stepwise mechanism This stepwise mechanism is supported by our inability to find transition state 54 computationally and the eventual isolation of a by-product. When trienoate 36 was treated with certain Lewis acids [e.g.…”