58105-23-0Relevant academic research and scientific papers
Atomic motions and protonation stereochemistry in nucleophilic additions to bicyclobutanes
Hoz, Shmaryahu,Azran, Carmela,Sella, Ariel
, p. 5456 - 5461 (2007/10/03)
Several nucleophilic reactions on bicyclobutanes activated at the gehead carbon by electron withdrawing groups (SO2Ph, CO2Me, COPh, and CN) were performed in MeOH. In all cases, the less stable 1,3-disubstituted cyclobutanes isomer was preferentially obtained (compared to the equilibrium ratio). The results for the two charge localizing groups CN and SO2Ph oppose the existing knowledge regarding the protonation stereochemistry of such carbanions. Ab initio calculations (6-31G*) have shown that as the nucleophile approaches the bicyclobutane, the bridgehead activating group moves inward toward an axial position. With a charge localizing group (CN and S(H)SO2) the carbanion remains pyramidal, whereas with C(H)=O as an activating group, the carbanion is nearly planar. It is suggested therefore that under conditions where the carbanion undergoes rapid protonation, it is trapped in its initial pyramidal geometry. Whereas, in cases where the lifetime of the carbamon is long enough to allow appreciable equilibration, protonation may result in a different product distribution. This hypothesis was tested by slowing down the protonation rates. As a result, the more stable isomer was indeed preferentially obtained.
Bridgehead substituents effect on the reactivity of bicyclobutane in its reactions with nucleophiles. A comparison with olefinic systems
Azran, Carmela,Hoz, Shmaryahu
, p. 11421 - 11430 (2007/10/02)
The reactivity of bridgehead substituted bicyclobutanes towards nucleophilic attack was compared with that of the analogous vinylic compounds. Ab initio calculations suggest that the substituents exert nearly the same energetic effects on the ground state of the two systems. The observed difference in the reactivity of the two systems stems, therefore, from the different nature of corresponding transition states.
