Palladium Mediated Formation of Δ1- and Δ2-Carbapenems by Cyclofunctionalization of 4-Allenylazetidinones and 4-(2-Propynyl)azetidinones.

Creative approaches towards the synthesis of 2,5-dihydro- furans, thiophenes, and pyrroles. One method does not fit all!

“…63 In the late 1980's Liebeskind and coworkers reported that palladium could catalyze this cyclization and that the resulting vinyl palladate could be cross-coupled in situ with an olefin (Y = vinyl). 64 Since then a number of halide, selenium and sulfur electrophiles have also been shown to aid this cyclization while at the same time incorporating a functional handle (Y = Cl, Br, I, PhS, PhSe). 65 This powerful transformation has been revisited in the last eight years as part of what could only be described as a gold 66 and silver 67 catalyst rush.…”

Addition of Metalated 3‐Alkyl‐Substituted Alkoxyallenes to Imines: Preparation of Tetrasubstituted 2,5‐Dihydropyrroles, Pyrrolidin‐3‐ones, and Pyrroles

“…Alternatively, cyclizations of allenyl alcohols or allenylamines can also be achieved by transition metal catalysis . In particular, copper, silver, palladium, and gold salts/complexes were employed as catalysts, often furnishing the corresponding heterocycles under mild conditions. Since our investigation was performed in the pre‐gold catalysis age,[6a] we used silver nitrate (0.2 equiv.)…”

Novel Cyclization Reactions of Aminoallenes

“…The construction of the bicyclic β‐lactam carbapenem nucleus using aminoallene chemistry is a formidable challenge. The seminal work from Liebeskind’s group in 1988 on the palladium‐promoted cyclizations of 4‐allenyl‐2‐azetidinones 70 to Δ 1 ‐carbapenems 71 is a nice example (Scheme ) 40. A more recent contribution includes the catalytic use of palladium‐base catalysts for the aminocyclization of allene‐substituted β‐lactams 72 to Δ 2 ‐carbapenems 73 (Scheme ) 41…”