Zeolite catalyzed selective deprotection of di- and tri-O-isopropylidene sugar acetals

Selective deprotection of tethered glycoderivatives with unsaturated spacer

“…This high yield simple reaction of catalytic nature which involves non-toxic, inexpensive and readily available reagents, complements well other similar synthetic methodologies (Szarek et al, 1986 ;Park et al, 1994 ;Gou é th et al, 1995 ;Ravikumar and Farquhar, 2002 ;Agarwal and Vankar, 2005 ;Catelani et al, 2006 ;Rajput et al, 2006 ;Procopio et al, 2007 ;Wuts and Greene, 2007 ;Bhaskar et al, 2008 ;Procopio et al, 2008 ;Xavier et al, 2009 ).…”

Useful methods for the synthesis of isopropylidenes and their chemoselective cleavage

“…Interestingly, increase in reaction time to 24 h resulted in complete hydrolysis of the isopropylidenes. As 1a reportedly undergoes hydrolysis to form an inseparable mixture 25 of 2,3-O-isopropylidene-D-mannofuranose and 2,3-O-isopropylidene-D-mannopyranose, we carried out deisopropylidenation of 1-O-benzyl derivative of 2,3:5,6-di-O-isopropylidene-D-mannofuranose (entry 11, Table 3) in our reaction condition, 26 to find that the terminal 5,6-O-isopropylidene ring cleaves in preference to the 2,3-O-isopropylidene moiety in excellent yields (94%) within 2 h. On the other hand, the 1,2:3,4-di-Oisopropylidene-a-D-galactopyranose (3a) undergoes complete hydrolysis under the reaction conditions and gave the starting Dgalactose quantitatively. Interestingly, for Shi's ketone (entry 13, Table 3), upon hydrolysis in our reaction conditions generated the 4,5-deprotected mono-O-isopropylidene derivative, 13b 27 suggesting that spiro-fused isopropylidene moiety is more stable than the internal isopropylidene acetal ring.…”