Stereo- and regioselectivity in an intramolecular nitrone-alkene cycloaddition of hept-6-enoses with a trans-acetonide blocking group.
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.
Shing
Tony K M
TK
Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, NT, China. tonyshing@cuhk.edu.hk
Wong
Wai F
WF
Ikeno
Taketo
T
Yamada
Tohru
T