Novel N-Phosphonio Imine-Catalyzed Epoxidation Reactions

N-silyloxaziridines: synthesis and use for electrophilic amination

N-Silyloxaziridines were synthesized for the first time. Their tert-butyldiphenylsilyl (TBDPS) derivatives were stable reagents that were prepared on a multigram scale in three steps and in 44% overall yield from the corresponding benzylamines. They were mild electrophilic aminating reagents that reacted at room temperature with diversely substituted primary and secondary amines to produce N-monoalkyl or N,N-dialkyl benzaldehyde hydrazones in 44-87% yield.

Synthesis of dihydrobenzisoxazoles by the [3 + 2] cycloaddition of arynes and oxaziridines

Dihydrobenzisoxazoles are readily prepared in good yields by the [3 + 2] cycloaddition of oxaziridines and arynes. The reaction involves an unusual cleavage of the C-O bond of the oxaziridine and tolerates a variety of substituents on the oxaziridine and the o-(trimethylsilyl)aryl triflate to form aryl-, heteroaryl-, alkyl-, and naphthyl-substituted dihydrobenzisoxazoles. The resulting halogen-substituted dihydrobenzisoxazoles are readily elaborated to more complex products using palladium-catalyzed crossing-coupling processes.

Structure and stereodynamics of aryldiimino derivatives

Aromatic diimino derivatives, having two N=CPh(2) moieties bonded at the 1,8 positions of the anthraquinone, anthracene, biphenylene, and naphthalene rings, have been investigated by variable-temperature NMR spectroscopy, X-ray diffraction, and DFT calculations. In all the compounds, the imino substituents are essentially orthogonal to the aromatic plane and the phenyl groups bonded to the C=N carbons are diastereotopic (i.e., cis or trans to the aromatic N-substituent of the N=C moiety). The barriers for the cis/trans interconversion of the phenyl groups by planar nitrogen inversion have been determined. In the cases of anthracene and anthraquinone derivatives, the presence of syn and anti conformers was detected, and their interconversion barriers, due to the Ar-N rotation, were measured. At very low temperature, restricted rotations of the phenyl groups, displaying barriers in the range 4.8-6.9 kcal mol(-1), were also observed for all compounds: the barriers for the rotation of the cis were found to be larger than for the trans phenyl groups.