Practical catalyst for cyclic metathesis. Synthesis of functional and/or enantiopure cycloalkenes

Article abstract of DOI:10.1021/ja00140a015

The oxo-tungsten complex trans-WOCl₂(OAr)₂ (Ar = 2,6-dibromophenyl) is prepared by reaction of WOCl₄ with 2 equiv of 2,6-dibromophenol. A variety of nonconjugated dienes are cleanly cyclized to the corresponding cycloalkenes using 2 mol % of this catalyst in combination with 4 mol % of tetraethyllead. All three components of the catalyst system are commercially available. The catalytic reactions are typically complete in 1 h at 90 °C and allow the synthesis of chiral cycloalkenes with little or no loss in optical activity. For example, (R)-and (5)-citronellene have been cyclized to the corresponding (R)- or (S)-3-methylcyclopentenes in 97% enantiomeric excess. The cyclization is compatible with a variety of functional groups including some ester, amide, and ether derivatives. Tri- (but not tetra-) substituted cycloalkenes could be prepared using this catalyst.