Novel transition metal catalysts for intramolecular ene-reaction

We have designed a new class of MII-catalysts, namely molybdenum and tungsten (II) complexes of the type PhCH2(Et)3N+[M(CO)4C1Br2]- and M(CO)5(OTf)2 (M = Mo or W), which induce intramolecular cyclization of olefinic aldehydes to afford products with a cis-configuration at the newly formed chiral centres in some cases. These catalysts can be tuned to drive the reaction either toward the end or Prins-type product (32 or 89). The latter reaction occurs via an anti addition of the carbonyl carbon and OH across the C=C bond, as evidenced by isotopic labeling. A chair-like transition state with an axial carbonyl oxygen is proposed to rationalise the stereoselectivities observed.