[reaction: see text] A new tandem reaction was developed for the carbocyclization reaction of propargylic zinc reagents. First, we have shown that zinc salt promotes the Brook rearrangement into the carbanionic species followed by a stereospecific Zn-ene-allene carbocyclization reaction to lead to the corresponding cyclopentylmethylzinc derivatives. A single diastereoisomer is formed, even when a tertiary and a quaternary center are linked in the process.
The zinc-catalyzed addition of various alkynes to acylsilanes followed by a Zn-Brook rearrangement and either the Zn-ene-allene or Zn-yne-allene cyclization led to the enantio- and diastereoselective formation of carbocycles in a single-pot operation.
New Tandem Zn-Promoted Brook Rearrangement/Ene-Allene Carbocyclization Reactions. -The new tandem methodology represents a unique and straightforward way to generate polysubstituted cyclopentylmethylzinc and cyclopentylidenemethylenezinc derivatives as single diastereomers under mild conditions. -(UNGER, R.; COHEN, T.; MAREK*, I.; Org. Lett. 7 (2005) 23, 5313-5316; Dep. Chem., Tech.-Isr. Inst. Technol., Haifa 32000, Israel; Eng.) -R. Steudel 13-080
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