An Efficient, Selective Hydrolysis of Terminal Isopropylidene Acetal Protection by Zn(NO₃)₂· 6H₂O in Acetonitrile

Abstract

Di-O-isopropylidene sugar derivatives (1a-9a) on treatment with a solution of Zn(NO 3 ) 2 ∑6H 2 O in acetonitrile, undergo regioselective hydrolysis to furnish the corresponding diols (1b-9b) in excellent yields.

Studies Directed toward the Stereoselective Synthesis of Cytospolide E

“…It was our great relief that Zn(NO 3 ) 2 ·6H 2 O was found to be effective. 23 An inseparable mixture of seco acids 39 and 39a was obtained, which was then subjected to crucial macrolactonization following the Yamaguchi protocol. 4d,16d A complex mixture was formed, which was subsequently desilylated with TBAF to get lactone 45 as the only isolable product with 22% yield.…”

“…This was then opened regioselectively with DIBAL-H to get the corresponding primary alcohol, which directly converted to the corresponding acid using TEMPO/BAIB. 4f Finally, the acid was subjected to selective acetonide deprotection in the presence of Zn(NO 3 ) 2 ·6H 2 O 23 to provide the requisite seco acid 48 in 34% overall yield (in five steps). The stage was set for crucial macrolactonization.…”

“…Next, we have tried different reagents (CSA, AcOH) in different conditions for selective deprotection of acetonide in the presence of TBS ether, but none of them functioned well. It was our great relief that Zn­(NO 3 ) 2 ·6H 2 O was found to be effective . An inseparable mixture of seco acids 39 and 39a was obtained, which was then subjected to crucial macrolactonization following the Yamaguchi protocol. , A complex mixture was formed, which was subsequently desilylated with TBAF to get lactone 45 as the only isolable product with 22% yield.…”

The Total Synthesis of Proposed Immunoactive Glycolipids from S. Pneumoniae and a Re-evaluation of Their Immunological Activity

“…Zinc nitrate hexahydrate in acetonitrile selectively hydrolysed the isopropylidene group of the glyceride to provide the diol. 24 Sequential esterification, relying on the increased reactivity of the primary alcohol over the secondary alcohol, with palmitic acid (at 0 ºC) and freshly prepared cis-Vaccenic acid (at ambient temperature due to a more sluggish reaction) 25 provided the fully protected diglyceride. Following the second esterification, the two anomers surprisingly separated easily by column chromatography as the Rf values, for the first time since 9 diverged significantly.…”

Synthesis of chimera oligopeptide including furanoid β-sugar amino acid derivatives with free OHs: mild but successful removal of the 1,2-O-isopropylidene from the building block

“…The selective deprotection of 5,6-O-isopropylidene acetals of d-Glc is described using protic acids: e.g., H 2 SO 4 (Rbaa et al 2020;Miljkovic 2009;Sukumar et al 1986), HClO 4 on silica gel (Agarwal and Vankar 2005), polyphosphoric acid on silica gel (Nikam and Gore 2020) or AcOH (Ma et al 2020;Pikas et al 2020;Ferreira et al 2020;Ravn et al 2019;Gruner et al 2002a, b;Yadav, Chander and Reddy 1992). The application of some Lewis acids was also reported, such as FeCl 3 •6H 2 O/SiO 2 (Kim et al 1986), CuCl 2 •2H 2 O (Iwata and Ohrui 1981), Zn(NO 3 ) 2 •6H 2 O (Vijayasaradhi, Singh and Aidhen 2000), Yb(OTf) 3 •H 2 O (Yadav et al 2001) just as BiCl 3 (Swamy and Venkateswarlu 2002). Alternative methods for the selective removal of the isopropylidene protection under relatively mild conditions were studied more recently as aqueous tert-butyl hydroperoxide (Maddani and Prabhu 2011), CBr 4 -photoirradiation (Chen et al 2004) and acid zeolites (Rauter et al 2010).…”