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

Enantiomerically pure five-membered ring nitrones derived from L-tarta ric acid via C2-symmetric O,O'-protected 3,4-dihydroxy pyrrolidines un dergo highly regio- and stereoselective cycloaddition reactions with r acemic 2,3-dihydro-1-phenyl-1H-phosphole 1-oxide and 1-sulfide. In all cases formation of only two diastereomeric cycloadducts is observed a nd their ratio (up to 10:1) is dependent on the size of the protecting groups in the nitrone and on the extent of conversion. The tricyclic cycloadducts feature 2,2'-connection of pyrrolidine and phospholane ri ngs and six contiguous stereogenic centers of which three are created and the one at phosphorus is kinetically resolved during the cycloaddi tion process. It is established that in the studied kinetic resolution s the stereoselectivity factor 8 = k(S)/k(R) exceeds the value of 10 ( up to 14) in the most favorable cases. In a properly tuned reaction bo th the diastereomeric cycloadducts and the enantiomerically enriched d ihydrophosphole derivative can be simultaneously obtained in satisfact ory chemical and optical yields.