A-Haloacetophenone derivatives

A novel and simple procedure was developed for the construction of fully substituted thiophenes (13S913). A series of a-haloacetophenone derivatives were converted into fully substituted thiophenes by treatment with sodium sulfide in the presence of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and sodium iodide in aqueous ethanol under aerobic conditions. 

Other classes of nickel-catalyzed [3+2] cycloadditions include the addition of 2-haloacetophenone derivatives to alkynes to produce indenol derivatives (Scheme 3-36). This process likely involves initial oxidative addition to the haloaromatic, followed by alkyne insertion and carbonyl addition. In this case, zinc powder serves as reducing agent to regenerate the active nickel(0) catalyst. A mechanistically intriguing cycloaddition that proceeds without the action of reducing agents is the direct formation of bicyclic products from the addition of unsaturated ketones with alkynes. This process likely involves initial metallacycle formation followed by unusual rearrangement steps unique to the requisite doubly unsaturated carbonyl component. 

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