Sidechain interchange

The 2-acetoxy- and 2-benzoxypenem 429, 430 were obtained by reaction of the 2-oxopenam precursor with the appropriate acid chloride (TEA, CH2CI2, from — 60 to 0 °C). These enol esters cannot be utilized for sidechain interchange reactions, as the corresponding carbapenems do upon attempted displacement with nucleophiles, they reverted back to the starting thiolactone... 

Instead, secondary and tertiary aliphatic aminopenems of general formula 437, 438 were obtained by sidechain interchange from 2-p-cyano- or p-nitro-phenoxypenems (368, R = CN or NO2) and the appropriate amine, according to an addition-elimination process analogous to the one occurring on 2-sulfinylpenems [202]. 

Mudlitol (2) presents the only reported instance of a polyol that shows a slow interchange between the complex and its components, probably owing to steric hindrance by the bulky sidechains. With lanthanides, but not with uni- and di-valent cations, separate lines are found in the spectrum for the complexed and the uncomplexed molecules, even at 99°. (Slow exchange was postulated for the complex of Cr with c/j-inositol, but the evidence presented is not conclusive.)... 

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