Hydroxyethyl sidechain

Tritylthioazetidinone-phosphoranes unsubstituted at C3, either racemic (from 4-acetoxyazetidinones) or optically active (from 6a-bromopenams), were key intermediates in the Bristol penem programme in fact, they proved good substrates for the introduction of the (li )-hydroxyethyl sidechain by the acetylation-reduction sequence [51a]. Hydroxyethylated argentiothioazetidin-ones 229 are no longer obtained by this way, but have retained their original... 

HPIX is one of the most unstable of the natural porphyrins commonly employed in the laboratory because of the presence of labile hydroxyethyl sidechains. Thus synthesis of polymers from HPIX must be accomplished rapidly and under mild conditions. 

Once the hydroxy functionalised imidazolium salt is formed, it can be deprotonised and reacted with various metal complexes to form (transition) metal carbene complexes. The hydroxy group ensures that the ligand can be coordinated even to metals that are normally reluctant to form stable carbene complexes. A good example is the deprotonation of a hydroxyethyl functionalised imidazolium salt with potassium hydride [36]. The potassium cation coordinates to the oxygen atom of the alkoxide sidechain and forms cubes as structural elements (see Figure 4.6). The carbene end then coordinates to the respective... 

Priihs et al. found an elegant application for a seemingly remote hydroxy group in the sidechain [43]. The remoteness of the hydroxy group implies a mode of introduction to the central imidazole ring different to the epoxide method developed by Arnold (hydroxyethyl) and Thiel (hydroxyhexyl). Indeed, Priihs et al. modilied the classic method of imidazo-lium salt synthesis by using a bromoalkane as carrier for the hydroxy functional group. In this way, they reacted A-mesityl imidazole with l-bromo-ta-hydroxyalkanes to obtain the... 

Chlorinolysis of the 0-protected hydroxyethyl compound 365e gave the 4R chloro epimer 366e exclusively [136]. This compound was used for the synthesis of 368f, a compound characterized by a quaternary ammonium group in the C2 sidechain [136]. The 5R penem intermediate 368e was obtained, in this case, by thermal equilibration. 

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