Packiarajan, Mathivanan and Maitra, Uday (1995) Asymmetric Diels-Alder Reactions of Chiral Acrylates of Cholic Acid Derivatives. In: Journal of Organic Chemistry, 60 (2). pp. 364-369.
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New steroid-based chiral auxiliaries 6, 9, and 12 have been synthesized from readily available cholic acid. These new chiral auxiliaries place the reactive and the shielding sites in a 1,5 relationship to each other. Diels-Alder reaction of cyclopentadiene with corresponding acrylate esters (7, 10, and 13) have been examined. Acrylates 7 and 10 yielded cycloadducts with 29-88% diastereomeric excess with excellent endo selectivity in the presence of an excess of Lewis acids such as AlCl3, BF3.OEt(2), FeCl3, SnCl4, TiCl4, and ZnCl2. Treatment of acrylate 7 with cyclopentadiene in the presence of BF3.OEt(2) at -80 degrees C gave the endo adduct (>99%) with 88% de. Lewis acid catalyzed and uncatalyzed reactions of acrylates 7 and 10 with cyclopentadiene yielded cycloadducts with opposite stereochemistry. The chiral auxiliary was recovered in a nondestructive manner only via iodolactonization. Acrylate ester of alcohol 12 did not show any selectivity in either catalyzed and uncatalyzed reactions with cyclopentadiene. The presence of a flat aromatic surface at C-7 of the steroid was found to be essential to effect high diastereoselection.
|Item Type:||Journal Article|
|Additional Information:||Copyright of this article belongs to American Chemical Society.|
|Department/Centre:||Division of Chemical Sciences > Organic Chemistry|
|Date Deposited:||26 Apr 2011 05:59|
|Last Modified:||26 Apr 2011 05:59|
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