Stereo- and Regioselectivity in an Intramolecular Nitrone-Alkene Cycloaddition of Hept-6-enoses with a trans-Acetonide Blocking Group

• Published in: Chemistry : a European journal 2009-03, Vol.15 (11), p.2693-2707
• Main Authors: Shing, Tony K. M., Wong, Wai F., Ikeno, Taketo, Yamada, Tohru
• Format: Article
• Language: English
• Subjects: alkenes; carbohydrates; cycloaddition; cycloheptanes; nitrones
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800867

From sugar to cycloadduct: The effect of the trans‐acetonide blocking group and the stereochemistry of the substituents on the regio‐ and stereoselectivity in the intramolecular nitrone–alkene cycloaddition (INAC) reaction of hept‐6‐enoses (see scheme) is reported and studied by using theoretical analysis. The positional effect of the trans‐acetonide blocking group and the effect of the stereochemistry of the substituents on the regio‐ and stereoselectivity in intramolecular nitrone–alkene cycloaddition (INAC) reactions of hept‐6‐enoses are reported. Hept‐6‐enoses with a 2,3‐trans‐acetonide group were reacted with N‐alkyl hydroxylamine to give a mixture of exo and endo cycloadducts (cyclohexanols and cycloheptanols, respectively). Complete formation of endo cycloadducts (cycloheptanols) was realized for the INAC reaction of hept‐6‐enoses containing a 3,4‐trans‐O‐isopropylidene ring. Similarly, reaction of a hept‐6‐enose possessing a 4,5‐trans‐acetonide group surprisingly afforded exo cycloadducts (cyclohexanols) exclusively. The regio‐ and stereochemical outcomes of these reactions were rationalized on the basis of transition‐state energies obtained by computation. From sugar to cycloadduct: The effect of the trans‐acetonide blocking group and the stereochemistry of the substituents on the regio‐ and stereoselectivity in the intramolecular nitrone–alkene cycloaddition (INAC) reaction of hept‐6‐enoses (see scheme) is reported and studied by using theoretical analysis.