ANALYSIS OF STEREOCHEMICAL AND PROXIMITY REQUIREMENTS FOR R2S-4 PARTICIPATION IN CARBONIUM ION REACTIONS . SOLVOLYSIS OF STEREOISOMERIC CAGED THIA ALCOHOL DERIVATIVES

The kinetics of acetolysis of the epimeric octahydro-1,3,5-ethanylylidene-2-thiacyclobuta[c,d]pentalen-7-yl and octahydro-6,2,5-ethanylyhdene-2H-cyclobuta[c,d][2]benzothiophen-7-yl tosylates have been measured. In buffered acetic acid, the endo tosylates solvolyze at a rate comparable to that of anti-pentacyclo[5.3.0.02,5.03,9.04,8]-decan-6-yl tosylate (10) thus indicating that the sulfur atom exerts no neighboring group participation effects. Strikingly, however, the exo tosylate in the ethano-bridged series solvolyzes 5564 times faster than 10 and the acetate of retained configuration is produced in quantitative yield. In the case of the exo-methano-bridged tosylate, only a 32-fold rate enhancement is observed and product analysis indicates that approximately 20% of the reaction occurs via a heterolytic fragmentation. A connection is drawn between the stereochemistry of the leaving group and the internuclear distance between the sulfur atom and the incipient carbonium ion center. The bearing of these results on precise proximity requirements for anchimeric assistance by an heteroatomic neighboring group is discussed. Further consideration is given to the various cations which are produced in these caged systems upon ionization. © 1969, American Chemical Society. All rights reserved.