Cyclization Cascades Initiated by 1,6-Conjugate Addition

Abstract

Dienyl diketones containing tethered acetates selectively undergo two different 1,6-conjugate addition-initiated cyclization cascades. One is a 1,6-conjugate addition/cyclization sequence with incorporation of the nucleophile, and the other is catalyzed by DABCO and is thought to proceed via a cyclic acetoxonium intermediate. The reaction behavior of substrates lacking the tethered acetate was also studied. The scope of both types of cyclization cascades, the role of the amine additive, and the factors controlling reactivity and selectivity in the two different reaction pathways is discussed.

Beyond the Divinyl Ketone: Innovations in the Generation and Nazarov Cyclization of Pentadienyl Cation Intermediates

“…[22] When R 1 was a pendant acetate group (R 1 = (CH 2 ) n CHR 2 OAc) and exposed to conditions incorporating 1,4-diazabicyclo[2.2.2]octane (DABCO), diastereopure bicycle 61 was unexpectedly obtained. This result was rationalized by the conjugate addition of DABCO to dienyl ketones of type 62 to form zwitterion 65 , which then undergoes an intramolecular S N 2 reaction to form 7-membered intermediate 66 (Scheme 12).…”

4π electrocyclisation in domino processes: contemporary trends and synthetic applications towards natural products

“…Frontier and colleagues envisaged the possibility of developing a Lewis acid-assisted tandem sequence comprising of 1,6-nucleophilic conjugate addition and 4π electrocyclisation. [54][55][56] They found that acetate containing dienyl diketones 146 and 148 follow two different 1,6-conjugate addition-promoted cyclisation cascades and generate the corresponding products 147 and 149 respectively (Scheme 22). 55,56 Lithium chloride and triethylamine have a substantial impact on the solubility of the catalyst.…”

“…[54][55][56] They found that acetate containing dienyl diketones 146 and 148 follow two different 1,6-conjugate addition-promoted cyclisation cascades and generate the corresponding products 147 and 149 respectively (Scheme 22). 55,56 Lithium chloride and triethylamine have a substantial impact on the solubility of the catalyst. A wide range of nucleophiles including primary amines, cyclic and acyclic secondary amines, malonate derivatives can be employed as external nucleophiles and more importantly, a single diastereomeric product is achieved in all cases.…”

“…The nucleophilic addition of pyrrolidine or dimethylmalonate to dienyl diketone 150 leads to a conventional 1,6addition and an adduct 151 is formed ( pathway A, Scheme 22). 55 Isomerisation and bond rotation of intermediate 151 furnishes the corresponding cationic intermediate 152, which undergoes regiospecific conrotatory 4π cyclisation to give richly functionalised 5-hydroxycyclopentenone 153. This cascade is of great synthetic interest because of the installation of all-carbon quaternary and contiguous tertiary stereogenic centres in an efficiently stereospecific manner.…”

Calcium Oxide Supported on Monoclinic Zirconia as a Highly Active Solid Base Catalyst

“…Extension to substrates 59 , each containing a substituent R 1 (Scheme ), enabled the synthesis of products 60 , containing adjacent quaternary centers 22…”