Reactions of the dione 1 and lactone 2 dimers of dimethylketene with the phosphoramidites (CH30)2PN(CH3)2 (3), CH3OP[N(CH3)2]2 (4), and CeHsOP[N(CH3)2]2 (5) and with trisdimethylaminophosphine (6) were investigated. Carboxy esters resulted from reactions of 3 and 4 with either dimer while 5 and 6 gave carboxamides. The structures of these products are similar to those formed from dimethylketene dimers on reaction with trialkyl phosphites. Except for reactions of 3, identical products were formed from either 1 or 2 and a given phosphorus derivative. On reaction of 1 and 3, three products are formed in relative proportions dependent on reaction temperature. These reactions are discussed in terms of a postulated mechanism involving nucleophilic attack by phosphorus on carbonyl carbon of 1 or 2, followed either by ring expansion to a cyclic pentacovalent phosphorus intermediate or by ring opening to a phosphonium enolate species. Isomerization of 1 to 2 in the presence of 5 or 6 is also accommodated by the suggested reaction series. Possible kinetic control of carboxamide vs. carboxy ester formation is treated in terms of the structures and reaction patterns predicted for the postulated pentacovalent intermediates. II), All show a weak ir band at about 1665 cm-1 for (4) R.
The reaction at -70°of dimethylketene with a wide variety of PXYZ gives a series of new 2:1 adducts containing pentacovalent phosphorus in a five-membered ring (5). Spectroscopic and chemical evidences for structure 5 are presented. Their preferred configurations from pmr spectra are discussed on the basis of trigonalbipyramidal structures. The relative stabilities of the series of adducts ( 5) are shown to be in accord with the expectations based on the strain and polarity rules. They are further shown to undergo clean reaction with water, methanol, CS2, C02, CH3I, and Br2 to give structurally novel products often in high yields.
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