Other One-Carbon Unit Equivalents

1-Dihalo-1-lithio species (halogenocarbenoids) undergo double insertion into the carbon-zirconium bonds of a zirconacyclopentane to produce, after hydrolysis,bicyclo[3.3.0]octanes (Eq. 51) [55]. 

Allenyl carbenoids (3-chloro-l-lithioalk-l-ynes) insert into zirconacy-clopentanes and zirconacyclopentenes to afford cyclic rj -allenyl/prop-2-ynyl zirconocene complexes which give cyclized-alcohol products on addition of aldehydes activated with boron trifluoride-diethyl ether (Eq. 52) [56]. 

Xi and coworkers reported a one-pot procedure for the preparation of highly substituted indenes, tetrahydroindenes, and cyclopentadienes via Lewis acid mediated reactions of zirconacyclopentadienes with aldehydes. The carbonyl groups of aldehydes were deoxygenated in the reaction and behaved formally as a one-carbon unit (Eq. 53) [57]. 

Acyl chloride was found to behave as a one-carbon unit when treated with zirconacyclopentanes and zirconacyclopentenes in the presence of CuCl. Cy-clopentene and cyclopentadiene derivatives were obtained, respectively (Eqs.54,55) [58,59]. 

Interestingly, propynoates and iodopropenoates can also behave as one-carbon unit equivalents to form 1,1-addition products. In the presence of CuCI, zirconacyclopentadienes react with iodopropenoatesto give cyclopentadiene derivatives (Eq.56) [60,61]. 

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