Oxazoles

Catalytic Amide Activation with Thermally Stable Molybdenum(VI) Dioxide Complexes

“…Oxazolines and thiazolines, and their oxidized analogs, oxazoles 1 and thiazoles, 2 are present in a myriad of bioactive natural products including thiopeptide antibiotics, 3 metal chelating siderophores, 4 and cyclic peptides (Scheme 1A). 5 Thiopeptides display high antibacterial activity and synthetic efforts that aim to explore their viability as therapeutics remain an active area of research.…”

“…Because incorporation of azolines can be a valuable method to activate amides, which is often difficult to achieve due to the low reactivity of the amide functional group, several synthetic strategies are known. 1,2 Azole and azoline containing natural products are often derived from peptides, and their biosynthesis involves selective dehydrative cyclization of cysteine, serine, or threonine residues. 24 In chemical synthesis, the oxazoline/thiazoline groups are introduced from 1,2-amino alcohols/thiols as the cyclization substrates through condensation of cysteine with nitriles, 25 oxyamination of alkenes, 26 and electrophilic cyclodehydration [27][28][29] with phosphorus-, [30][31][32][33] sulfur-, [34][35][36][37] and Ti(IV)based reagents.…”

Catalytic Amide Activation with Thermally Stable Molybdenum(VI) Dioxide Complexes

“…;1 H NMR (300 MHz, CDCl 3 ) δ 3.78 (s, 3H), 3.71 (d, J = 11.3 Hz, 1H), 3.11 (d, J = 11.3 Hz, 1H), 2.86 (p, J = 6.9 Hz, 1H), 1.52 (s, 3H), 1.21 (dd, J = 6.9, 1.1 Hz, 6H);13 C{ 1 H} NMR (75 MHz, CDCl 3 ) δ 178.0, 174.0, 83.8, 52.8, 41.1, 34.0, 23.9, 21.25, 21.16; HRMS (ESI+) m/z calculated for C 9 H 15 NNaO 2 S + [M + Na] + 224.0716, found 224.0725.…”

“…;1 H NMR (300 MHz, CDCl 3 ) δ 7.68 (dd, J = 3.7, 1.2 Hz, 1H), 7.50 (dd, J = 5.0, 1.2 Hz, 1H), 7.10 (ddd, J = 5.0, 3.7, 0.5 Hz, 1H), 4.94 (dd, J = 10.5, 7.8 Hz, 1H), 4.74−4.66 (m, 1H), 4.65− 4.55 (m, 1H), 3.82 (s, 3H); 13 C{ 1 H} NMR (75 MHz, CDCl 3 ) δ 171.4, 162.0, 131.3, 130.7, 129.3, 127.7, 69.9, 68.6, 52.7; HRMS (ESI +) m/z calculated for C 9 H 9 NNaO 3 S + [M + Na] + 234.0195, found 234.0205.…”

“…;1 H NMR (300 MHz, DMSO-d6) δ 8.11 (d, J = 8.1 Hz, 1H), 7.47−7.23 (m, 5H), 6.37 (d, J = 4.7 Hz, 1H), 5.22 (dd, J = 6.1, 5.3 Hz, 1H), 4.99 (d, J = 4.7 Hz, 1H), 4.38 (dt, J = 8.1, 4.1 Hz, 1H), 3.82 (ddd, J = 11.1, 6.1, 4.3 Hz, 1H), 3.68 (ddd, J = 11.1, 5.3, 3.9 Hz, 1H), 3.62 (s, 3H); 13 C{ 1 H} NMR (75 MHz, DMSO-d6) δ 172.5, 171.3, 141.5, 128.4, 128.0, 127.5, 73.8, 61.7, 54.5, 52.4; HRMS (ESI+) m/z calculated for C 12 H 15 NNaO 5 + [M + Na] + 276.0842, found 276.0853. Methyl (MoO 2 (6-MePic) 2 under O 2 atmosphere): Compound 33 (50.6 mg, 0.200 mmol), MoO 2 (6-MePic) 2 (…”