Reactions of 6-diazopenicillanates with allylic sulphides, selenides, and bromides

Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement

“…However, such high stereoselectivity has not been achieved in reactions with penicillanates. The reaction of 6-diazopenicillanate ( 259 ) with allylic sulfides or selenides in the presence of a catalyst gave a complex mixture, the major product being (+)- 261a , formed by the rearrangement of ylide 260 (Scheme ). − The copper catalyst gave higher yields of the desired 6,6-disubstituted penicillanates and no 6α-monosubstituted product 261c was formed. Sulfides appeared to give better diastereoselectivity than selenides.…”

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.…”

“…Since the discovery of derivatives of olivanic acid 249 and thienamycin, the synthesis of penicillin analogues with a carbon side chain at C 6 has attracted considerable attention. The transition metal-catalyzed reaction of 6-diazopenicillinates with allyl sulfides represents a convenient method for synthesizing these 6-substituted penicillin analogues. , Addition of copper(II) acetylacetonate to a mixture of phenyl allyl sulfide and 6-diazopenicillinate ( 536 ) in dichloromethane resulted in the formation of 6,6-disubstituted penicillinates 538 and 539 (Scheme ). This result can best be interpreted as proceeding by the initial formation of sulfonium ylide 537 which undergoes a subsequent [2,3]-sigmatropic rearrangement.…”