REACTIVITY OF CYCLIC ARSENITES AND PHOSPHITES - X-RAY STRUCTURES OF BIS(5,5-DIMETHYL-1,3,2-DIOXARSENAN-2-YL) ETHER AND T-BUTYL-12H-DIBENZO[D,G][1,3,2]DIOXARSENOCIN-6-YL) ETHER

Reaction of the chlorophosphite CIPOCH(2)CMe(2)CH(2)O 1 with cyclohexy lamine gave the expected product (C6H11NH)POCH(2)CMe(2)CH(2)O 3 wherea s the corresponding chloroarsenite 2 led to the bridged compound 12. W hen the reaction was performed in the presence of water, 1 gave the ex pected product H(O)POCH(2)CMe(2)CH(2)O 11 whereas 2 gave the ore-bridg ed compound (AsOCH(2)CMe(2)CH(2)O)(2)O 13. The amino phosphite 3 under went hydrolysis to afford the ring cleaved product 18 whereas the phen oxy phosphite 21 led to the ring preserved compound 11. In contrast, t he corresponding phenoxy arsenite (PhO)AsOCH(2)CMe(2)CH(2)O 25 gave th e oxo-bridged compound 13. Addition of perchloro-o-benzoquinone to the phosphite 23 was highly exothermic and afforded the phosphorane 29; h owever the corresponding arsenonate 27 reacted very sluggishly at room temperature and when heated gave an uncharacterizable mixture of prod ucts. The identity of the title oxy-bridged compounds 13 and 15 obtain ed here has been confirmed by X-ray structure determination; the six-m embered rings in 13 have a 'chair' conformation and the eight-membered rings in 15 have a 'symmetrical anti' conformation.