116005-25-5Relevant academic research and scientific papers
Conformations of Saturated Six-Membered Ring Phosphorus Heterocycles. 2-Aryl-1,3,2λ5-oxazaphosphorinanes
Bentrude, Wesley G.,Setzer, William N.,Sopchik, Alan E.,Chandrasekaran, Subramanian,Ashby, Michael T.
, p. 7119 - 7127 (2007/10/02)
A series of 2-aryl-2-oxo- and 2-thioxo-5-tert-butyl-1,3,2λ5-oxazaphosphorinanes has been prepared (6-12).Assignments of cis or trans geometries to individual diastereomers were made by 31P and 1H NMR criteria combined wit X-ray crystallographic structures for cis-8 and trans-12. 1H NMR analysis at 300 MHz of chair ->/0 (chair -> twist) for the 2-oxo series cis-6, cis-8, cis-11, and cis-12 (N3H/PPh, N3H/PMes, N3Ph/PPh, N3Ph/PMes).Substitution of H on N3 by Ph (cis-11) changes the ΔG0 (chair -> twist) value for the PPh compound (cis-6) by 0.9 kcal/mol in favor of the twist form.The same substitution for Mes case (cis-8) results in an even greater change (>/= 2.2 kcal/mol) in ΔG0 (chair -> twist) with cis-12 in fact essentially completely in twist conformation 15.Methyl substitution at N3, cis-9, likewise increases the population of twist conformation, clearly an effect of destabilizing N3Me/PPh interactions in the chair, which are relieved in the twist conformation.These results point to the major role of N3R/PZ steric repulsive effects in the equilibria of 1,3,2λ5-oxazaphosphorinanes.Excluded is the possibility that Ph substitution at N3 merely reduces the importance of n/?* anomeric effects involving the N3 lone pair and axial substituent Z (Ar, Me2N) on phosphorus.The trans diastereomers also readily depopulate the chair conformation to give twist form 16, however, instead of 15 (trans-6,8, and 11).The pseudoaxial-seeking tendencies of substituents on phsophorus for trans diastereomers are shown to be CH3O > Ph > Me2N.A notable finding for the trans-2-aryl-2-oxo-5-tert-butyl-1,3,2λ5-oxazaphosphorinanes is the destabilizing effect of equatorial PMes compared to equatorial PPh, which results in greater depopulation of the diequatorially substituted chair, 13.
Influence of ortho Methyl and Isopropyl Substituents on the Reactivity of N-t-Butyl P-Arylphosphonamidic Chlorides with Isopropylamine and t-Butylamine: Steric Acceleration of Metaphosphonimidate Formation by an Elimination-Addition Mechanism; Contrasting Behaviour of N,N-Dimethyl P-A...
Freeman, Sally,Harger, Martin J.
, p. 1399 - 1406 (2007/10/02)
The two types of phosphonamidic chloride ArP(O)(Cl)NMe2, (5) and ArP(O)(Cl)NHBut (7) have been prepared with Ar=Ph, o-MeC6H4, 2,4,6-Me3C6H2, and 2,4,6-Pri3C6H2.Both types give the expected phosphonic diamide substitution products with PriNH2 and ButNH2 in MeCN, but the two types display contrasting reactivity.With ButNH2 the NMe2 substrates (5) become progressively less reactive as the degree of steric crowding increases, and although the decrease is quite small (70-fold overall) it seems consistent with an associative N2(P)> mechanism.These substrates react >=100 times faster with PriNH2, than with ButNH2 and in PriNH2-ButNH2 competitive experiments they give almost exclusively (>=99percent) the product derived from the less hindered PriNH2.For the NHBut substrates (7) with ButNH2, there is little difference in reactivity between the Ph and o-MeC6H4 compounds, and between the 2,4,6-Me3C6H2 and 2,4,6-Pri3C6H2 compounds, but remarkably the more crowded pair of substrates is the more reactive, by a factor of ca. 100.Also, in competitive experiments these substrates display relatively little preference for reaction with PriNH2.Here a dissociative elimination-addition mechanism, with a metaphosphonimidate intermediate, is seen to be important.A possible explanation of the steric acceleration is advanced.The ability of (7; Ar=Ph) to undergo substitution by elimination-addition makes possible the phosphonylation of unreactive nucleophiles such as ButOH and Pri2NH under mild conditions.
