Electrophilic Cyclization of 1,5‐Enynes

Abstract

Valuable six‐membered carbocycles including highly substituted benzenes, 1,4‐cyclohexadienes, and 4‐fluorocyclohexenes can be prepared from simple 1,5‐enynes by iodonium‐induced cyclization. This cyclization strategy was applied to the total synthesis of cybrodol, a sesquiterpenoid with a pentasubstituted aromatic core (see scheme).

Halocyclization of o-(alkynyl)styrenes. Synthesis of 3-halo-1H-indenes

“…This result shows that a direct halocyclization has occurred, probably through the formation of a stabilized carbocation 2 that undergoes proton elimination to afford the functionalized indene moiety (Scheme 1). It should be noted that in contrast to those examples recently reported by Kirsch and co-workers that proceed through a 6-endo cyclization process, 5 our reaction implies an unprecedented 5-endo halocyclization reaction of an enyne derivative. 8 The stability of the tertiary carbocation intermediate 2 could be the key for the success of the proposed 5-endo cyclization.…”

“…Remarkably, the use of olefins 4 for triggering this type of cyclization reactions has remained unknown until very recently, when Kirsch and co-workers have established that 1,5-enynes can undergo an iodoniuminduced carbocyclization via 6-endo-dig processes. 5 On the other hand, we have recently described the (enantioselective) synthesis of 1H-indene derivatives by an unprecedented gold(I)-catalyzed 5-endo-dig cyclization of ortho-(alkynyl)-styrenes 1. 6 In this context, and considering that the presence of an halogen atom at the C-3 position of the final indene derivative could be of interest for further functionalization, we wondered about the feasibility of synthesizing 3-halo-1H-indenes 7 from the same o-(alkynyl)styrenes 1 as proposed in Scheme 1.…”

1,3-Dien-5-ynes: Versatile Building Blocks for the Synthesis of Carbo- and Heterocycles

“…1), 90 and Barrett has reported a related procedure for the synthesis of 4H-1,3-benzodioxin-4-ones from a particular type of 1,3-dien-5-ynes employing ICl (Scheme 18, eq. 2).…”

Alkynylcyclopropanes from Terminal Alkynes through Consecutive Coupling to Fischer Carbene Complexes and Selective Propargylene Transfer

“…Chromatographic purification provided cycloadducts 11 a-c in good yields. Overall, a new transformation of 1,6-enynes has been accomplished that comprises consecutive www.chemeurj.org C À C coupling and cycloisomerization without the assistance of any electrophilic initiator (iodine [14] or Group 10 and 11 metals, [15] Scheme 6).…”