Carbon-derivatized

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

It must be pointed out that the heterofuUerenes discussed above are not available today, and may never be available owing to synthetic limitations or unexpected instability not predicted in the above-mentioned theoretical studies. In comparison to carbon bucky balls, the chemistry of heterofuUerenes might have more important implications. Development of molecular engines and computers, derivatization for drug delivery, and applications in material science might be new scientific areas involving these interesting molecules. 

Recently, Uneyama reported that treatment of (R)-l-tosyl-2-trifTuoromethylazir-idine 76 (Scheme 3.24) with w-BuLi at -100 °C and subsequent trapping of the anion with electrophiles such as chloroformates produced aziridine-2-carboxylates 77 in good to excellent yields [71]. The retention of the configuration of the tri-fluoromethylated quaternary carbon center in the course of the reaction was confirmed by derivatization of the product and by X-ray studies. 

Cyclization of substituted phenylacetylene sequences afforded functionalized macrocycles that were amenable to subsequent manipulation. For example, transesterification of 42 with octanol in the presence of 18-crown-6 ether and potassium carbonate gave the corresponding ester in 85% yield (Scheme 13). The ester functionalities could be reduced by DIBALH to give the hydroxymethyl-substituted macrocycle (43) in 61 % yield. The low yield of this particular transformation is attributed to mechanical losses during purification, due to the highly polar nature of the product. Macrocycle 43 could then be treated with alkyl bromides to give a group of benzyl ether derivatized PAMs. 

Reactions of Free and Derivatized Carboxylic Acids and Carbon Dioxide... 

---