New spiro derivatives of penicillin

Terminal methylene phosphonium ions: precursors for transient monosubstituted phosphinocarbenes

“…The analogous Buchner ring expansion reactions, involving benzene derivatives and transient carbenes or complexes thereof, has been widely used to introduce cycloheptatriene rings into natural products and materials. 62–69 Similar intramolecular ring expansions were reported for other transient main-group carbene analogues, such as silylenes, 70–76 and phosphinidenes. 77 Attempts to trap the transient carbene by performing the deprotonation at −40 °C in fluorobenzene in the presence of 2 bar dihydrogen or carbon monoxide, both known to react with electrophilic carbenes, 78–80 were unsuccessful.…”

Cascade Processes of Metallo Carbenoids

“…Sulfur ylides are useful intermediates in synthetic chemistry and have been utilized for the synthesis of a number of β-lactam antibiotics, − pyrrolizidine alkaloids, , and other natural products .…”

“…Interest in the chemistry of β-lactam antibiotics continues to thrive . The tandem cyclization−rearrangement reaction of carbenoids with sulfur atoms has also been applied to the conversion of the penicillin nucleus into cephalosporin derivatives by a number of research groups. − One example involves the reaction of 4-thioazetidinone 505 with dimethyl diazomalonate in the presence of rhodium(II) acetate to give sulfide 507 in good yield 233,234 (Scheme ). Formation of this product can be explained by carbenoid addition to the sulfur atom producing sulfonium ylide 506 which then undergoes a [1,2]-shift.…”

6-Diazopenicillanates. Part 1. Reactions with furans

“…1 1 Hz for the 2-isomers and ca. 15 Hz for the E-isomers. There is no coupling observable across the y,6-bond and the stereochemistry of the latter was deduced by application of the Tobey-Simon rules,' which predict the yproton to be ca.…”