SYNTHESIS AND INVESTIGATIONS OF [OXAZOLO[2,3-A]ISOINDOL-9B(2H)-YL]PHOSPHONATES AND [OXAZOLO[2,3-A]ISOINDOL-9B(2H)-YL]PHOSPHINATES - A NEW CLASS OF HETEROCYCLES

We attempted to synthesize diethyl (1-methyl-2-phthalimidoethyl)phosphonate (14a) in a Michaelis-Becker reaction using diethyl sodiophosphonate (13) and the tosylate 12a of (2-hydroxypropyl)phthalimide as starting materials. Instead of TsO substitution in 12a by the nucleophile 13, the carbonyl C-atom of the phthalimido moiety was attacked by 13, followed by an intramolecular nucleophilic substitution at C(2) of the side chain leading to the (oxazolo[2,3-a]isoindolyl)phosphonate 15a (Scheme 1). Similarly, 12a and N-(2-bromoethyl)phthalimide (12b) reacted with butyl (benzene)sodiophosphinate (18) to the (oxazolo[2,3-a]isoindolyl)(phenyl)phosphinates 20a and 20b, respectively (Scheme 2). The attempt to synthesize enantiomerically pure 2-substituted (2-phthalimidoethyl)phosphonates 27 starting from L-alpha-amino-acids failed, too (Scheme 3): the main products of the reaction of the NN-phthaloyl-O1-tosyl-L-aminoalcohols 25a-d with 13 were the 3-substituted (oxazolo[2,3-a]isoindolyl)-phosphonates 26a-d, the desired 27b and 27c being observed as by-products in the P-31-NMR spectrum.