The scope of silver nitrate‐catalyzed cycloaddition of arenediazonium salts has been expanded to include aryl‐ and alkylsulfonyl diazomethanes as well as the recently introduced diazomethyl sulfonamides. The reliance on these two classes of diazo compounds led to a new synthetic approach to the rare 2‐aryltetrazol‐5‐yl sulfones as well as to the synthesis of hitherto not described 2‐aryltetrazol‐5‐yl sulfonamides.

Thermally promoted tandem Wolff rearrangement -Staudinger [2 + 2] cycloaddition of α-cyano-α-diazo ketones and imines afforded 3-cyano-β-lactams in good to excellent yields as one diastereomer. The process represents the first example of generating cyanoketenes via the Wolff rearrangement of diazo compounds. The reaction is virtually insensitive to the substitution pattern in both reaction partners. It afforded high product yields even for imines bearing bulky tertiary alkyl substituents at the imine's nitrogen atom, which is indicative of the reaction proceeding predominantly as the concerted [2 + 2] cycloaddition rather than stepwise N-acylation -ring closure process. Examples of reductive manipulation of the resulting 3cyano-β-lactams are provided opening an entry into 3aminomethyl 2-azetidinones and azetidines.

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Screening of a library of novel N-hydroxylactams amenable by the Castagnoli-Cushman reaction identified four lead compounds that facilitated 55Fe transport into P. aeruginosa cells (one of these synthetic siderophores was found to be as efficient at promoting iron uptake as the natural siderophores pyoverdine, pyochelin or enterobactin). Conjugates of the four lead siderophores with ciprofloxacin were tested for antibacterial activity against P. aeruginosa POA1 (wild type) and the ∆pvdF∆pchA mutant strain. The antibacterial activity was found to be pronounced against the ∆pvdF∆pchA mutant strain grown in CAA medium but not for the POA1 strain. This may be indicative of these compounds being ‘Trojan horse’ antibiotics. Further scrutiny of the mechanism of the antibacterial action of the newly developed conjugates is warranted.

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