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CHM216PSIII - give apparently supra-supra[2 2 addition...

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CHEM 216 Problem Set III 1. i) Addition of borane (BH 3 ) and dichlorocarbene (:CCl2) to alkenes is believed to occur via a concerted pericyclic mechanisms. Are these allowed or forbidden pericyclic reactions? Is your answer consistent with the observed reactivity? Explain your reasoning ii) Some other carbenes also add to double bonds but via a stepwise radical mechanism. What about electronic structure of these carbenes might result in a change in mechanism? How might you determine experimentally which reaction pathway is occuring? iii) The molecule below undergoes rapid addition to dienophiles such as PTAD and TCNE to
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Unformatted text preview: give apparently supra-supra [2+2] addition products (Brook, D. J. R.; Haltiwanger, R. C.; Koch, T. H., J. Am. Chem. Soc. 1992, 114, 6017). Explain N N O O CN CN NC NC N N N Ph O O TCNE PTAD N N O O N N O O CN CN NC CN N N O O Ph 2. The bridged radical below has been suggested as an intermediate in the photochemical decar-bonylation of 3-phenyl propanal. Suggest experiments to test this hypothesis CH 2 H 2 C 3. Irradiation of the cyclic ketone below with light at 321 nm converts it quantitatively to the trans isomer. Explain. (hint: build a model of the product) O O 321 nm...
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