title: Acetylenic Vinyllithiums: Consecutive Cycloisomerization-[4 + 2] Cycloaddition Reactions.
abstract: Acetylenic vinyllithiums (2), which were generated from the corresponding acetylenic vinyl bromides (3) by low-temperature lithium-bromine exchange, cyclize on warming to give, following quench with water, isomerically pure conjugated bis-exocyclic 1,3-dienes (1) in good to excellent yield. Both five-membered and six-membered outer-ring dienes may be prepared: 5-exo closure of an acetylenic vinyllithium, which proceeds with total stereocontrol via syn-addition to give the E-isomer of a five-membered outer-ring diene, tolerates aryl-, silyl-, or alkyl-substituents at the distal acetylenic carbon; the corresponding 6-exo process is less facile and seems to be confined to substrates bearing an anion-stabilizing substituent, such as phenyl or trimethylsilyl, at the terminal acetylenic carbon. The highly reactive bis-exocyclic 1,3-dienes serve as precursors to polycyclic materials through subsequent Diels-Alder reaction with a wide variety of dienophiles. The consecutive exchange-cyclization-cycloaddition methodology, which can be conducted in one pot without isolation of intermediates, provides an efficient, operationally simple, and diastereoselective route to diverse polycyclic ring systems.
authors.affiliation: Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-4060, and the Department of Chemistry, Connecticut College, New London, Connecticut 06320-4196.
authors.forename: William F.
authors.initials: WF
authors.lastname: Bailey
authors.forename: Nanette M.
authors.initials: NM
authors.lastname: Wachter-Jurcsak
authors.forename: Mark R.
authors.initials: MR
authors.lastname: Pineau
authors.forename: Timo V.
authors.initials: TV
authors.lastname: Ovaska
authors.forename: Rachel R.
authors.initials: RR
authors.lastname: Warren
authors.forename: Carl E.
authors.initials: CE
authors.lastname: Lewis