Kinetic Resolution in 1,3-Dipolar Cycloaddition of Tartaric Acid-Derived Nitrones to 2,3-Dihydro-1-phenyl-1H-phospholes. An Enantioselective Approach to the 2,2'-Coupled Pyrrolidine-Phospholane Ring System
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Abstract
Enantiomerically pure five-membered ring nitrones derived from L-tartaric acid via C2-symmetric\n0,O'-protected 3,4-dihydroxy pyrrolidines undergo highly regio- and stereoselective cycloaddition\nreactions withracemic2 ,3-dihydro-l-phenyl-VI-phosphol1e- oxide and 1-sulfide. In all cases formation\nof only two diastereomeric cycloadducts is observed and their ratio (up to 1O:l) is dependent on the\nsize of the protecting groups in the nitrone and on the extent of conversion. The tricyclic cycloadducta\nfeature 2,2'-connection of pyrrolidine and phospholane rings and six contiguous stereogenic centers\nof which three are created and the one at phosphorus is kinetically resolved during the cycloaddition\nprocess. It is established that in the studied kinetic resolutions the stereoselectivity factors = k s l k ~\nexceeds the value of 10 (up to 14) in the most favorable cases. In a properly tuned reaction both\nthe diastereomeric cycloadducts and the enantiomerically enriched dihydrophosphole derivative can\nbe simultaneously obtained in satisfactory chemical and optical yields.
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