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DOI: 10.1055/sos-SD-221-00001

Gao, S.; Wang, D.Science of Synthesis: Metal-Catalyzed Cyclization Reactions, (2016132.

Nickel-catalyzed alkenylchromium cyclizations have been used for the construction of cyclic compounds, from common rings to medium-sized and macrocyclic rings. Treatment of alkenyl iodide 29 with 5 equivalents of chromium(II) chloride in the presence of a catalytic amount of nickel(II) chloride in dimethylformamide at room temperature for 40 hours gives the cyclized product 30 in 79% yield as a single diastereomer (Scheme 21).[‌82‌] The diastereoselectivity is controlled by a chair-like transition state 31, in which the benzyloxy and the chromium(III) alkoxide groups must be antiperiplanar to avoid an unfavorable allylic 1,3-strain between the quasi-equatorial chromium alkoxide and the alkene. Investigation of nickel-catalyzed alkenylchromium cyclization using model substrates, as shown in Table 7, demonstrated the importance of steric effects on the cyclization.[‌82‌]

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