Chemoselective oxidation of primary alcohols catalysed by Ce(III)-complex intercalated LDH using molecular oxygen at room temperature

Herein we describe the preparation of an efficient heterogeneous catalyst consisting of an anionic Ce(III)-complex immobilized Zn/Al-layered double hydroxide (LDH) and its use in the catalytic liquid phase oxidation of primary alcohols using molecular O(2) at room temperature. Various primary alcohols could be transformed to their corresponding aldehydes in good to excellent yields using the set of optimal conditions. The heterogeneous catalytic system can also be recovered and reused for several cycles without a significant loss of catalytic activity.     

Influence of (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold: stereoelectronic control of the persistence of o-quinonoid reactive intermediates of photochromic chromenes

Regioisomeric photochromic chromenes 1Ch-6Ch substituted with the (2,3,4,5,6-pentamethyl/phenyl)phenyl scaffold were designed to delve into stereoelectronic effects on the spectrokinetic properties of photogenerated o-quinonoid reactive intermediates. While the latter derived from 1Ch, 2Ch, 4Ch, and 5Ch were found to exhibit notable persistence, those from 3Ch and 6Ch were found to revert rapidly at room temperature to preclude visible coloration. The intermediates of 1Ch and 2Ch were found to be marginally more stable than those of 4Ch and 5Ch, respectively, attesting to the possibility of toroidal conjugation via C(ipso)-π orbitals in the former. The rapid reversion of the intermediates of 3Ch and 6Ch is attributed to unfavorable electronic repulsion between the phenyl ring of the (pentamethyl/phenyl)phenyl scaffold and one of the lone-pairs of the o-quinonoid oxygen. Thus, the regioisomerically substituted photochromic chromenes are shown to permit control of the reversion, very rapidly as well as slowly, of the colored o-quinonoid intermediates through operation of stereoelectronic effects differently.