New tandem Zn-promoted Brook rearrangement/ene-allene carbocyclization reactions.

[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.