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: 5aa=10.306(1), b=11.875(1), c=11.221(1) Å, β=112.992(7)°, Z=4; 5ba=7.386(1), b=17.094(2), c=8.557(1) Å, β=114.208(9)°, Z=4. The structure of 5a contains methanol disordered over a centre of symmetry. The crystal of 5b was twinned.