Reactions of acyl phosphonates with organoaluminum reagents and hetero diels-alder reactions with unactivated dienes

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2014
Hossain, Md. Shakhawoat
α-Hydroxy phosphonates medicinally important compounds due to broad spectrum of biological activities. Addition reaction of commercially available trialkylaluminum reagents (trimethylaluminum and triethylaluminum) to benzoyl and alkanoyl phosphonates were investigated. Nucleophilic Me3Al solely gave tertiary α-hydroxy phosphonates in good yields. On the other hand, when Et3Al addition was carried out at 0 °C hydride addition product rather than ethyl addition was isolated in good yields. When the temperature was lowered to -100 °C , Et3Al addition was achieved but in low yields. We have also investigated the addition reactions of trialkynylaluminum reagents, mainly triethynyl, tris-propynyl and tris-phenylethynyl, to benzoyl and akanoyl phosphonates to synthesize tertiary α-hydroxy propargylic phosphonates. Addition of triethynylaluminium gave the propargylic compounds in low to moderate yields (15-67%). Addition of tris-propynyl and tris-phenylethynyl reagents formed the expected products in moderate to good yields (30-75%). In all cases, electronic features of the aromatic unit affected the chemical yield. Presence of an electron-withdrawing group on the phenyl ring provided the product in better chemical yield. When benzoyl and alkanoyl phosphonates were compared in terms of yields, first one formed the product in better yields at a shorter reaction times. vi Hetero Diels-Alder (HDA) reaction is an important reaction for the construction of the pyranosyl unit of many biologically active compounds. HDA reactions of acyl phosphonates with 2,3-dimethyl-1,3-butadine were investigated to prepare glycosyl type phosphonates. To activate the HDA reaction, several Lewis acids were tested. AlCl3 was found to be the most effective catalyst by forming glycosyl phosphonates in acceptable to good yields (40-79%) depending on the acyl phosphonates.

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Citation Formats
M. S. Hossain, “Reactions of acyl phosphonates with organoaluminum reagents and hetero diels-alder reactions with unactivated dienes,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.