Tightly Convoluted Polymeric Phosphotungstate Catalyst:  An Oxidative Cyclization of Alkenols and Alkenoic Acids

Abstract

[reaction: see text] A tightly convoluted polymeric phosphotungstate catalyst was prepared via ionic assembly of H3PW12O40 and poly(alkylpyridinium). An oxidative cyclization of various alkenols and alkenoic acids was efficiently promoted by the polymeric catalyst in aq H2O2 in the absence of organic solvents to afford the corresponding cyclic ethers and lactones in high yield. The catalyst was reused four times without loss of catalytic activity.

Preparation and characterization of poly[acrylamide‐co‐3‐(acryloylamino)propyldodecyldimethylammonium bromide]/polyoxometalate composite microspheres

“…However, the electrostatic interaction between APDDAB and PW 12 O 40 3− in the P(AM‐ co ‐APDDAB)/PW 12 O 40 composite microspheres was dominant. 21–23 With regard to the aforementioned conclusion that PW 12 O 40 3− was mainly located at the surface of the composite microsphere, we speculated that APDDAB in the P(AM‐ co ‐APDDAB) microgels was mainly distributed at the surface. So, the composite microspheres had a core–shell structure and amphiphilic features, which are useful in phase‐transfer catalysis.…”

“…Crosslinking between PW 12 O 40 3− with alkyl quaternary ammonium cations of grafted polymers has been reported. 21–23 The resultant product was essential for crosslinking the polymers through phosphotungstates and an amphiphilic, crosslinked, and supramolecular insoluble complex. The materials reported in the literature were bulk (nonstructured) materials; however, the material we prepared presented a core–shell structure.…”

“…The remarkable features of the composite microspheres were that both the catalyst and aqueous phase could be simultaneously separated from the reactive system. Yamada and coworkers 21–23 prepared a series of hydrogel composite materials via poly({[3‐(acryolylamino) propyl]dodecyldimethylammonium nitrate}‐ co ‐( N ‐isopropylacrylamide) 12 ) crosslinked by polyoxotungstates. Additionally, these materials were efficient catalysts for the oxidation of alkenes, amines, and sulfides.…”

Oxidative cyclization of alkenols with Oxone using a miniflow reactor

“…We therefore decided to turn our attention to developing an oxidative cyclization of alkenols [32–33] for the preparation of furanyl and pyranyl alkyl carbinols. During our investigation, we found that the oxidative cyclization of ( Z )-4-decen-1-ol ( 1a ) with Oxone (2KHSO 5 ·KHSO 4 ·K 2 SO 4 ) proceeded at 80 °C without any exogenous catalysts under small-scale batch conditions (up to 50 mmol of 1a ) to give threo -1-(2-tetrahydrofuranyl)hexan-1-ol ( 2a ) in 99% yield within 5 min (Table 1) [34].…”

“…When a mixture of an aqueous solution of Oxone (100 mM, 1 mL, 2 equiv vs 1a ) and a 2-propanol solution of 1a (50 mM, 1 mL) was stirred at 80 °C for 5 min, the cyclization took place very smoothly to afford threo -1-(2-tetrahydrofuranyl)hexan-1-ol ( 2a ) in 99% yield as a single racemic diastereoisomer. Yet when 30% aq H 2 O 2 was used as the oxidant at 80 °C, the cyclization hardly proceeded at all, even with a longer reaction time [32]. We had previously found that a polymeric phosphotungstate catalyst promoted the cyclization of 1a with 30% aq H 2 O 2 at 50 °C with a much longer reaction time (24 h).…”