CHEM 432 Midterm: CHEM 432 midterm432_2009
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Provide the product, reactant, or reagent for four of the foll owing five reactions. If you attempt all five, be sure to cross out the one you don"t want me to mark. Provide a reasonable mechanism for one out of the following two transformations. / 10: silyl groups have the ability to stabilize positive charges at the position to the silicon group (the so-called silicon -effect ). This effect was exploited by scott denmark"s group to convert a series of bis-alkylidene ketones (1) to functionalized cyclopentenes (2) in high yield. Surprisingly, when trienyl ketones (1a) were used, the anticipated product (2a) was not formed instead, the unexpected product 3 was isolated. Provide mechanisms to account for the formation of 2 and 3. In words, briefly summarize how it is that stoltz is able to correct the stereochemistry at the chiral quaternary centres, in proceeding from 2 to: bonus marks for using (appropriately) the word steroablative !
