Pinacol reaction with carbenes

Harrity and co-workers described the application of 2-substituted 1-alkynylboronic esters in the Dotz cycloaddition of Fisher chromium carbene complexes, affording in a highly regioselective fashion a novel class of hydroxy-naphthyl boron pinacolates (entry 18, Table 1.3) [217]. These reaction products also provided, upon treatment with ceric ammonium nitrate, the corresponding quinone boronic esters. 

A similar reaction sequence accounts for the formation of 1,l-dichloro-2,2,3,3-tetramethylcyclopropane in 15% yield from the reaction of pinacol with dichloro-carbene. Likewise, reaction of m 5o-dihydrobenzoin with dichlorocarbene gave a 15% yield of cw-stilbene [10] (Eq. 3.7). 

Catalytic enantioselective allylic substitutions of aiyl- and alkyl- substituted phosphates (63) with commercially available allenylboronic acid pinacol ester (64) resulted in the formation of tertiary or quaternary C-C bonds. Reactions were promoted by sulfonate-bearing chiral bidentate Af-heterocyclic carbene (NHC) complexes of copper (66), which exhibited the unique ability to furnish chiral products arising from the Sj.,2 mode of addition. Allenyl-containing products (65) were generated in up to 95% yield, >98% 8 2 selectivity and 99 1 enantiomeric ratio (Scheme 21). ... 

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