Cascade reactions hydride compounds

Several helical polycyclic aromatic hydrocarbons bearing aryl substituents at the most sterically hindered position were synthesized in an efficient three-step cascade reaction. The initial benzannulated enediynes were synthesized by the reaction of appropriate lithium acetylenides with an aryl-rert-butyl ketone. This was followed by reduction of the resultant acetylenic propargyl type alcohol with triethylsilicon hydride. This method turned out to be particularly successful for the synthesis of helical molecules. The reaction of ketones 3.588 and 3.590 with the lithium derivative of l-ethynyl-2-(2-penylethynyl)benzene 3.545 or related binaphthyl derivative followed by reduction and three-step sequence of cascade reactions led to polycyclic aromatic compounds 3.589 and 3.591, respectively, in a good yield (Scheme 3.48) [294, 295]. 

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. 

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