Competing sulfonylation and phosphonylation following rearrangement of an O-sulfonyl-N-phosphinoylhydroxylamine with tert-butylamine: demonstration of a phosphonamidic-sulfonic anhydride intermediate and 18O-labelling evidence on how it may be formed1

Abstract

Reaction of R(Ph)P(O)N HOSO2Bn (R = PhMeCH) with Bu(t)NH2 in CH2Cl2 gives a mixture of RP(O)(NHPh)-NHBu(t) and Bu(t)NHSO2Bn, the proportion of the sulfonamide increasing steadily (14.6% to 32.9%) as the concentration of amine is reduced (8.0 to 0.2 mol dm(-3)). Apparently the phenyl and sulfonate groups in the substrate become transposed, giving a phosphonamidic-sulfonic anhydride RP(O)(NHPh)OSO2Bn which then reacts at the phosphorus or sulfur atom to give the final products; an authentic sample of the anhydride gives similar mixtures of products. Substrate labelled with 18O in the sulfonyl position (57 mol% one 18O atom) gives sulfonamide containing most but not all of the label (43.7 mol% one 18O atom with 2.0 mol dm(-3) amine). This implies partial equilibration of the three sulfonate oxygen atoms during rearrangement, or after the anhydride intermediate has been formed.

Use of an 18O-labelled phosphonamidic-sulfonic anhydride to learn more about the mechanism by which O-sulfonyl-N-phosphinoylhydroxylamines rearrange

“…In our earlier study the 18 O label was confined to the SO 2 group of the hydroxylamine derivative 4 (R = PhMeCH) but was shared in the product between the sulfonamide 6 (76% of the available 18 O) and the phosphonamidate 7 (R = PhMeCH). 3 ¶ We inferred that the label in the anhydride intermediate 5 (R = PhMeCH) was shared in the same way between the SO 2 group and the bridging O atom but then struggled to relate the labelling pattern to a reasonable mechanism for the rearrangement of 4 to 5. In the present study the similar anhydride 5 (R = Bu t ) (sample A) gives products in which the label is shared between 6 (78% of the 18 O in the anhydride) and 7 (R = Bu t ) in much the same way even though the label is all in the SO 2 group of the anhydride to begin with.…”

“…By measuring the distribution of the label between the products 6 and 7 resulting from attack at sulfur, the distribution of 18 O (SO 2 vs. SOP) in the anhydride intermediate 5 could, we supposed, be deduced. 3 The results, however, were not consistent with any straightforward transposition mechanism. Our concern now is with the possibility that the distribution of the label in the anhydride intermediate might not be the same when it reacts as when it is formed.…”

“…In principle, the anhydride intermediate could be attacked at sulfur instead of phosphorus but in only one case (Scheme 1, R = PhMeCH) has appreciable competition been seen. 3 That observation opened the way to an investigation of the transposition mechanism using the hydroxylamine derivative 4 (R = PhMeCH) labelled specifically with 18 O in the sulfonyl (SO 2 ) group. By measuring the distribution of the label between the products 6 and 7 resulting from attack at sulfur, the distribution of 18 O (SO 2 vs. SOP) in the anhydride intermediate 5 could, we supposed, be deduced.…”

Organophosphorus Chemistry

“…It involves acylation of ethyl-1,1-bisphosphonate (202) with trifluoroacetic anhydride, addition of selected Reformatsky reagents to the resulting 1-trifluoroacetyl-1,1-ethyl bisphosphonates (203) and finally spontaneous Horner-Wadsworth-Emmons (HWE) olefination of the adducts (Scheme 55). 106 The first synthesis of phosphonoacrolein (209) was achieved by acid decomposition of b-ethoxy-a-(methoxymethyl)vinylphosphonate (210) derived from lithiated phosphonate (211) and chloromethyl methyl ether (MOMCL) (Scheme 58). With unsymetrically substituted dienes mixture of regioisomers are obtained.…”

“…correspond to attack of tert-butylamine at sulphur and phosphorus atoms of the anhydride (Scheme 110) 211. …”