6ji-electrocyclization

In the context of developing rapid access to thioaurone structures, De and coworkers observed an interesting 6ji-electrocyclization/isomerization cascade. The reaction of sulfanyl amide 257 with an excess of LDA and cinnamaldehyde produced thioaurone 258 in 83% yield (Scheme 47) (03SL1479). On heating at 210 °C, compound 258 isomerized to give 259, which underwent a subsequent electrocyclization reaction to produce 260. A formal [l,3]-hydride shift then furnished the observed product 261. 

However, the substitution pattern on the arene is crucial for the success of the Heck reaction. When a second Heck coupling takes place in an ortho position of another alkenyl unit, cyclization of the intermediately formed palladium complex may occur. Hence, formation of alkylideneindanes and alkylindenes, especially under classical Heck conditions with phosphines in the catalyst cocktail, was observed (Scheme 5-22). Alternatively, 6ji-electrocyclization/oxidation might occur to yield naphthalenes or related compounds. ... 

Clearly, the acid-catalyzed E to Z isomerization of the hydrazone carbon-nitrogen bond in 28 must precede cych-zation. There are two possibiUties for the mechanism that can either be described as a 6ji-electrocyclization or as an... 

Sorensen and coworkers used a domino conrotatory electrocydic ring-opening/ 6ji-disrotatory electrocyclization for the formation of ring C in the total synthesis of ( )-viridin (4-327) (Scheme 4.72) [112]. Heating 4-325 in the presence of a base followed by in-situ oxidation with DDQ afforded the tetracyde 4-326 in 83% yield. 

The scope and device application of the 6ji-photoinduced electrocyclization of aromatic systems continue to expand and, as in recent years, the reactions of... 

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