| +Br2\H+. enol formation, than attack of the enol with +Br2 carbonyl group in the alpha-bromo-keton is less basic, the enolisation will proceed 'only', if
all alpha-halogenketon molecules are exhausted (the Section called Halogenisation in Chapter 2)
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| secondary orbital interactions explains endo product cyclopentadien is planar. In the intermediate transition state an envelope conformation can be supposed Diels-Alder-Reaction,
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supra-supra-facial cyclo-addition
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| ,
photochemical allowed
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| -CO2, -tert-pentyl-carbon-acid +H2SO4, hydrolisis of the ketal
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