C→N Migrations of the ethoxycarbonyl group in reactions of ortho-substituted aryl isocyanates with the 1,3-zwitterion derived from triisopropylphosphine and ethyl 2-cyanoacrylate

The reactions of meta—para-substituted aryl isocyanates with phosphorus-containing 1,3-zwitterions, which proceed with the CN migration of the CO₂Et group to form the corresponding carbamates, were extended to ortho-substituted aryl isocyanates. The influence of the steric and electronic effects of the ortho substituents in the aromatic rings of aryl isocyanates on the ease of this rearrangement is qualitatively considered.     

Synthesis of P‐Unsymmetrically Substituted Derivatives of NAPHOS

2, 2′‐Bromomethyl‐1, 1′‐binaphthyl reacted with di‐tert‐butylphosphine to form (R, S)‐4, 4‐di‐tert‐butyl‐4, 5‐dihydro‐3Hdinaphtho[2, 1‐c:1′, 2′‐e] phosphepinium bromide 5a . The di‐iso‐propyl‐ ( 5b) and the phenyl‐ethyl ( 5c ) analogue of compound 5a were prepared by similar routes. Treatment of 5a with potassium diphenylphosphide, KPPh₂, afforded the corresponding bis‐phosphine, 2‐di‐tert‐butylphosphino‐methyl‐2′‐diphenylphosphino‐methyl‐1, 1′‐binaphthyl 6 . An attempt at the synthesis of the first example of a bis‐phosphonite ligand with a 2, 2′‐dimethyl‐1, 1′‐binaphthyl backbone unexpectedly led, in the first step, to 2, 2′‐bis[diethylamino‐methoxy‐phosphino]‐1, 1′‐binaphthyl 9 . X‐ray crystal structure analyses were carried out for the phosphepinium bromides 5a and 5c , and for the bis‐phosphines 6 and 9 . In compounds 5a and 5c the interplanar angle between the two parts of the binaphthyl group is 65.8° and 64.5°, respectively, as reflected in the conformation of the seven‐membered ring. In 5a the bromide and methanol residues are hydrogen‐bonded to form Br^— (···HOCH₃)₂ units. In 6 the binaphthyl interplanar angle is 86.1°; the two halves of the molecule show appreciably different conformations of the ring substituents, as do those of 9 (binaphthyl angle 78.6°).