Rapid Entry into Mono-, Bi-, and Tricyclic β-Lactam Arrays via Alkene Metathesis

4-Acetoxy-2-azetidinone and (3 R,4 R )-4-acetoxy-3-[(1 R )-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 (3 R,4 R )-4-acetoxy-3-[(1 R )-1-( tert -butyldimethylsilyl)-oxyethyl]-2-azetidinone were converted into β-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 β-lactam alkenes with styrene partners and ring closing metathesis of β-lactam dienes using the Schrock [(CF 3 ) 2 MeCO] 2 Mo( CHCMe 2 Ph)( NC 6 H 3 -2,6- iso -Pr 2 ) ( 1 ) or Grubbs Cl 2 (Cy 3 P) 2 Ru CHPh ( 2 ) carbenes gave diverse monocyclic and bicyclic β-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 β-lactam conjugated dienes as exemplified by the conversion of (3 S,4 R )-(−)-3-[(1 R )-( tert -butyldimethylsilyl)oxyethyl]-1-(5-oxa-oct-7-en-2-yn-1-yl)-4-(2-propenyl)azetidin-2-one ( 83 ) into (6 R,7 S )-(+)-7-[(1 R )-( tert -butyldimethylsilyl)oxyethyl]-3-[(2,5-dihydro)-3-furanyl]-1-azabicyclo[4.2.0]oct-3-en-8-one ( 98 ).