Rapid entry into mono-, bi-, and tricyclic β-lactam arrays via alkene metathesis

4-Acetoxy-2-azetidinone and (3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyl)-oxyethyl]-2-azetidinone were converted into 4-alkenyloxy-, 4-(N-allyltoluene-4-sulfonamido)-, 4-(allylthio)-, and 4-alkenyl-2-azetidinone systems. In addition, 4-acetoxy-2-azetidinone and (3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyl)-oxyethyl]-2-azetidinone were converted into beta-lactam dienes via sequential C-4 substitution using unsaturated alcohols, allyl mercaptan, N-allyltoluene-4-sulfonamide, and allyl(chloro)dimethylsilane followed by N-allylation. Crossed metathesis of beta-lactam alkenes with styrene partners and ring closing metathesis of beta-lactam dienes using the Schrock [(CF3)(2)MeCO](2)Mo(=CHCMe2Ph)(=NC6H3-2,6-iso-Pr-2) (1) or Grubbs Cl-2(Cy3P)(2)Ru=CHPh (2) carbenes gave diverse monocyclic and bicyclic beta-lactam systems including derivatives of 1-azabicyclo[4.2.0]octan-8-one, 1-azabicyclo[5.2.0]nonan-9-one and its 6-thia, 6-aza, and 6-oxa analogues, 7-oxa-1-azabicyclo[6.2.0]octan-10-one, 8-oxa-1-azabicyclo[7.2.0]octan-11-one, and 9-oxa-1-azabicyclo[8.2.0]octan-12-one. Ring-closing enyne metathesis and tandem ring-closing enyne and diene metathetic reactions were used to produce bicyclic beta-lactam conjugated dienes as exemplified by the conversion of (3S,4R)-(-)-3-[(1R)-(tert-butyldimethylsilyl)oxyethyl]-1-(5-oxa-oct-7-en-2-yn-1-yl)-4-(2-propenyl)-azetidin-2-one (83) into (6R,7S)-(+)-7-[(1R)-(tert-butyldimethylsilyl)oxyethyl]-3-[(2,5-dihydro)-3-furanyl]-1-azabicyclo[4.2.0]oct-3-en-8-one (98).