Hydroxamic acids and their derivatives—II

Lossen Rearrangements under Heck Reaction Conditions

“…Similarly, heating a mixture of phenyl isocyanate and 8a in THF/CH 2 Cl 2 (1:1) for 1 h affords the O-car-bamoylhydroxamate (17) in 65% yield (Scheme 6). [21] During a Lossen rearrangement, 17 forms as an undesired side product that arises from the consumption of two equivalents of hydroxamic acid as one equivalent condenses with the isocyanate ( Table 4). These results provide examples of one-pot amine trapping of isocyanates generated by base or metal-mediated Lossen rear-rangements and show the future synthetic utility of these transformations.…”

“…Similarly, heating a mixture of phenyl isocyanate and 8a in THF/CH 2 Cl 2 (1:1) for 1 h affords the O ‐carbamoylhydroxamate ( 17 ) in 65% yield (Scheme ) 21. During a Lossen rearrangement, 17 forms as an undesired side product that arises from the consumption of two equivalents of hydroxamic acid as one equivalent condenses with the isocyanate ( 3 , Scheme ).…”

“…A solution of 8a (1.4 g, 10 mmol) and phenyl isocyanate (1.2 g, 10 mmol) in dichloromethane (1 mL) and THF (1 mL) was heated on a water‐bath for 1 h. After cooling and adding n ‐hexane, crude product was obtained 21. Recrystallization from ethyl acetate afforded 17 as short white needles; yield: 1.7 g (65%); R f =0.7 (methanol/chloroform, 5%); mp 180 °C (reported: mp 181–182 °C);39 1 H NMR (300 MHz, DMSO): δ =12.42 (s, 1 H), 10.41 (s, 1 H), 7.91 (d, 2 H, J =7.51 Hz), 7.58–7.53 (m, 5 H), 7.34 (t, 2 H, J =7.79 Hz), 7.08 (t, 2 H, J =7.49 Hz); 13 C NMR (75 MHz, DMSO): δ =165.09, 152.36, 138.23, 132.22, 131.13, 128.97, 128.61, 127.36, 123.19, 118.41.…”

“…A solution of 8a (1.4 g, 10 mmol) and phenyl isocyanate (1.2 g, 10 mmol) in dichloromethane (1 mL) and THF (1 mL) was heated on a water-bath for 1 h. After cooling and adding n-hexane, crude product was obtained. [21] Recrystallization from ethyl acetate afforded 17 as short white needles; yield: 1.7 g (65%); R f = 0.7 (methanol/chloroform, 5%); mp 180 8C (reported: mp 181-182 8C); [39] Preparation of N-(Benzoyloxy)benzamide (16): [22] A solution of 8a (500 mg, 3.65 mmol, 1 equiv.) and potassium tert-butoxide (409 mg, 3.65 mmol, 1 equiv.)…”