Five-membered heterocycles metallation regioselectivity

Chiral carbo- and heterocycles are widespread structural motifs in biologically active compounds. The cycloisomerization of 1,6-dienes (A) offers an elegant and atom-economic [56] approach to five- or six-membered carbo- or heterocycles [57]. Metal complexes based on Pd [58], Ni [59], Rh [60], Ru[61], and Ti[62] have been identified as promising lead structures for catalyst development. Some of the reported systems are highly chemo- and regioselective toward the formation of the individual five-membered ring compounds B-D (Scheme 2.1.5.2). Enantioselec-tive cycloisomerization, however, has been assessed only sparsely so far, and remains a challenging task [46, 63]. 

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