Abstract
The reaction of CpW(CO) 3 Na with a number of propargyl bromides with tethered aldehydes and ketones afforded η 1 -propargyl species that were subsequently transformed into tungsten-η 3 -2-(methoxycarbonyl)allyl compounds upon treatment with p-TSA/CH 3 OH; the overall yields exceeded 60%. Sequential treatment of these tungsten-η 3 -allyl complexes with NOBF 4 and NaI in CH 3 CN led to intramolecular allyltungsten-carbonyl cyclization, yielding fused α-methylene butyrolactones of five-, six-, and seven-membered carbocyclic rings. All the reactions proceeded with high diastereoselectivities except for 9-methylene-7-oxabicyclo[4.3.0]nonan-8-one (22) and 10-methylene-8-oxabicyclo[5.3.0]decan-9-one (23). Modification of the metal center with a chloride ligand led to significant improvement of the trans-stereoselection of 22; the chloride modification did not significantly enhance stereoselection of 23. The stereochemical course of the reaction products is rationalized on the basis of a bicyclic transition-state mechanism.