Molecular structure of 4-methoxy-2,3-dimethyl-2,4- dihydro[1,2]benzoxaphosphinino-[4,3-c]pyrazole-4-oxide and its carboxylic analogues

The crystal structures of 5a 4-methoxy-2,3-dimethyl-2,4-dihydro[1,2]benzoxaphosphinino-[4,3-c]pyrazole-4-oxide and 5b 2,3-dimethyl[1]benzopyrano[4,3-c]pyrazol-4-one have been determined by 31P and 1H NMR study and single-crystal X-ray diffraction. The progress of conversion of chromone 1a was monitored by 31P NMR. After 24 h two additional signals of 4a and 5a could be seen in NMR spectrum. Both compounds crystallise in monoclinic system in space group P21/c. The crystal data are: 5a aZ10.306(1), bZ11.875(1), cZ11.221(1) A ° , bZ112.992(7)8, ZZ4; 5b aZ7.386(1), bZ17.094(2), cZ8.557(1) A ° , bZ114.208(9)8, ZZ4. The structure of 5a contains methanol disordered over a centre of symmetry. The crystal of 5b was twinned. q 2004 Elsevier B.V. All rights reserved.