Abstract
The reaction of ((di-iso-propyl)amino)(chloro)phosphenium cation [i-Pr2N-P-Cl]+ (1) with phenyl cyclopropane afforded cis- and trans-l-diisopropylamino-2-phenyl-phosphetane-1-oxide (3a-cis and 3a-trans), and -1-thion (4), respectively. The cis-1-diisopropylamino-2-(p-substituted-phenyl)-3-methyl-phosphetane-1-oxides (3b – 3d) were obtained in excellent yields unexpectedly from the similar reactions of trans-2-methyl-1-(p-substituted-phenyl)-cyclopropane. The six new compounds have been characterized on the basis of elemental analysis, IR, 1H, 31P NMR and MS. The configurations of 3a-cis, 3a-trans and 3c were elucidated by 2D NOESY. Molecular structure of 2-p-methylphenyl-3-methyl-phosphetane-1-oxide (3c) has been established by X-ray crystallography: in 3c, 1-diisopropylamino group is cis to 2-p-methylphenyl group as well as the dihedral angle between the planes C(l)-P-C(3) and C(1)-C(2)-C(3) is 15.09°, which is the least in the found values. A carbocation mechanism including the attack of P+ on less hindered carbon on cyclopropane ring and the cation-π interaction between the positive P+-N of 1 and benzene ring portion of 2 is proposed. The single-crystal data: primitive orthorhombic, space group Pbca(#61), a = 20.053(2), b = 13.955(2), c = 12.526(4), V = 3505(1) Å3, Z = 8, DC = 1.09 g cm−3, F(000) = 1280.00, λ(Mo-Kα) = 0.71069 Å, μ(Mo-Kα) = 1.50 cm−1. Refinement with 182 parameters and 1138 independent reflections with I > 3.00 σ (I) in the range 2° < θ < 25.0° gave R = 0.051 and RW = 0.055.
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