Diels-Alder cycloadditions of 2-pyrones and 2-pyridones

A Mechanistic Study of the Lewis Base-Directed Cycloaddition of 2-Pyrones and Alkynylboranes

“…This prereaction complex then undergoes ligand exchange to generate bis(alkynyl)borane ID and a molecule of BF 3 . Inspection of the transition state (TS1M) of this process shows that this reaction involves a concerted mechanism via a four-membered ring involving two threecentre two-electron bonds (Scheme 2).…”

“…and BF 3 While there does not appear to be a very significant driving force for the equilibration of all possible cycloadducts to the aryldifluoroborane, the presence of excess Lewis acid (remaining after consumption of alkyne during cycloaddition) probably serves to drive this transformation forward. To investigate this further, the energy profile of the equilibration of mono-and di-alkynylated cycloadducts was studied and is depicted in Schemes 8 and 9, respectively.…”

“…In both cases, similar trends were obtained. Alkyne substrates bearing phenyl-, n butyl-and t butyl-substituents reacted rapidly under mild conditions to give the corresponding functionalised aromatic products 7, 12-19 in good to excellent yields (entries [1][2][3][4][5][6][7][8]. The combination of thiazole-substituted 2-pyrone 20 and TMS-alkyne 11 resulted in a slower reaction and this process was conducted at slightly elevated temperature, resulting in some protodesilylation of the product.…”

Synthesis of 2H-pyran-2-ones and fused pyran-2-ones as useful building blocks

“…Found: C, 67.24;H, 7.20;N, 7.97;IR (KBr, cm -1 ) 3460, 3345, 2930, 1690, 1634 C, 68.37;H, 7.82;N, 7.25. Found: C, 68.28;H, 7.78;N, 7.34;IR (KBr, cm -1 ) 3435, 3331, 2924, 2852, 1686, 1636, 1611 3,25.7,28.6,28.9,29.4,30.0,115.5,116.8,131.0,149.9,161.2;MS m/z: 193 9, 55.4, 114.2, 118.4, 123.0, 127.1, 127.9, 128.3, 128.9, 130.2, 132.4, 133.8, 151.6, 159.3, 160 8, 55.80, 55.88, 111.1, 112.0, 118.3, 121.4, 122.7, 126.9, 127.5, 128.4, 128.7, 132.2, 133.5, 148.7, 148.9, 151.5, 159.8, 165.8 8, 109.2, 117.4, 122.6, 135.2, 137.3, 145.6, 149.3, 149.6, 158.7 …”

Functionalization of N-tosyl-2-pyridinone with silyl ketene acetal catalyzed by Lewis acid, and synthetic studies of corynantheidol

“…8 In these areas, elegant methods for the functionalization of pyridine rings using chiral 1-acylpyridinium salts as substrates have been developed by Comins' research group, 5,6 and the syntheses of many biologically active natural products were also reported. 9 In comparison with the significant efforts in studies of the 4-alkoxypyridine derivatives, the researches involving the reactivity of the 2-oxypyridine (2-pyridinone) derivatives have mainly been limited to the Diels-Alder reactions 10,11 and, to the best of our knowledge, the introduction of the acetate units into oxygenated pyridine derivatives has been reported only once. 5 As part of our continuous program for the development of new methodologies for heterocyclic compounds, 12 we focused our attention on the utilization of the activated 2-pyridinone derivatives.…”