Efficient synthesis and crystal structure of 2-propyl-5-(substituted)phenyl-1,4-dioxo-1,2,3,4,5,6,7,8-octahydro-[1,4,2]diazaphosphorino[1,2-a] [1,3,2]benzodiazaphosphorine 3-oxides

In order to search for novel antitumor and antiviral agents with high activity and low toxicity, some 2-propyl-5-(substituted)phenyl-1,4-dioxo-1,2,3,4,5,6,7,8-octahydro-[1,4,2]diazaphosphorino[1,2-a][1,3,2]benzodiazaphosphorine 3-oxides (2a–e) have been designed incorporating the proximate carbonyl and phosphoryl groups into the benzoannulated phosphadiamide heterocycle and synthesized in acceptable yields. These compounds contain the proximate carbonyl and phosphoryl groups in the fused heterocycle. Their structures were confirmed by spectroscopic methods and microanalyses. The results from X-ray crystallography analysis of 2a showed that the proximate carbonyl and phosphoryl groups are not coplanar because of their being jointly located in the fused heterocycle, having ring tension, and this then destroys the conjugation between the CO and the PO moieties. As a result, the length of the PC bonds measured as 1.851(3)–1.852(3) A are just the same as that of a PC bond not involved in conjugation (1.80–1.85 A). Also,the C(1), C(2), C(3), N(2), N(3), and P(1) atoms of the [1,4,2]diazaphosphorino moiety exist preferably in the boat conformation. The coplanar C(1), C(3), N(2), and N(3) atoms, within an average deviation of 0.0102 A, form the ground floor of the boat conformation, whereas the P(1) and C(2) atoms are on the same side of the coplanar structure with the distance of 0.7067 and 0.6315 A, respectively. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:63–71, 2002; DOI 10.1002/hc.1107