Combined Directed ortho Metalation−Halogen Dance (HD) Synthetic Strategies. HD−Anionic ortho Fries Rearrangement and Double HD Sequences
摘要:
A general and efficient directed ortho metalation (DoM)-halogen dance (HD)-electrophile quench sequence for the synthesis of trisubstituted pyridyl O-carbamates is described. A second HD sequence furnishes highly functionalized tetrasubstituted pyridines. Furthermore, a hitherto unobserved double HD rearrangement is reported. Under similar LDA conditions, aromatic O-carbamates with OMe, Cl, and F substituents (4a-c) undergo either a HD-electrophile quench sequence, 4a-c -> 18-20, or a HD-anionic ortho Fries rearrangement, 4a-c -> 6a-c, respectively.