Combined directed ortho metalation-halogen dance (HD) synthetic strategies. HD-anionic ortho fries rearrangement and double HD sequences.
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.