Calcium-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols Derived from Donor–Acceptor Cyclopropanes

Abstract

A calcium-catalyzed, dehydrative, ring-opening cyclization of (hetero)aryl cyclopropyl carbinols is reported. The cyclopropyl carbinols are prepared directly from the corresponding donor-acceptor (D-A) cyclopropanes. The calcium catalyst catalyzes the formation of putative (hetero)aryl cyclopropyl carbinyl cations that undergo ring-opening to allylcarbinyl cations. Subsequent intramolecular Friedel-Crafts reaction affords (hetero)aryl-fused cyclohexa-1,3-dienes in up to 97% yield. This approach represents the first example of catalysis for this intramolecular, dehydrative ring-opening cyclization and outperforms the previous reports using stoichiometric Lewis acids.

Carbon–Carbon and Carbon–Heteroatom Bond-Forming Transformations Catalyzed by Calcium(II) Triflimide

“…France and co-workers also exploited Ca(NTf 2 ) 2 in a homo-Nazarov-type cyclization 24 to access 1,2-dihydronaphthalenes through the rearrangement of a cyclopropyl carbinol unit (Scheme 12). 25 A similar reactivity had been previously reported by Nishii et al, but the reactions required stoichiometric amounts of Lewis acid. 26…”

Stereochemical Courses and Mechanisms of Ring-opening Cyclization of Donor–Acceptor Cyclopropylcarbinols and Cyclization of 7-Benzyloxy Dibenzyl Lignan Lactones

“…4f Recentry, France and co-workers improved our method by using a catalytic amount of Ca(NTf 2 ) 2 instead of a stoichiometric amount of BF 3 ¢OEt 2 or Sc(OTf ) 3 . 5 Although the modified method can provide a variety of cyclic compounds, this method deals with racemic substrates. Meanwhile, the mechanism of the reaction has not been revealed, and two plausible mechanisms can be proposed.…”

“…Following our previously reported transformation 4a of dichlorocyclopropane, the desired substrates 1a and 1b were obtained in good yields. However, cyclopropanations of (E)-and (Z)-1-phenyl-1-propenes using α,α-diazo-β-ketoester in the presence of the Rh 2 (esp) 2 catalyst used in France's report, 5 or other catalysts such as Rh 2 (OAc) 2 , Cu(acac) 2 , and Cu(OTf ) 2 , failed to afford desired cyclopropanes due to the stereocongestions. 7,8 Treatment of 1a with BF 3 ¢OEt 2 produced 2a in 72% yield as a single isomer (Scheme 4).…”

Synthetic Routes to Electroactive Organic Discotic Aromatic Triazatruxenes

“…An expansion study by Eva and co‐workers has combined N‐(hetero)arylmethyl derivatives of heptacyclic compound 10,15‐dihydro‐5 H ‐diindolo[3,2‐a:3′,2′‐ c ]carbazole (triindole) ( 26a – h ) and examined the conformation in the solid state for three derivatives ( 26b , 26c , and 26e ) (Scheme ). The X‐ray crystallographic examination for all three compounds indicated that the molecules expect a tropical conformation with all of the elastic arms concentrating in the direction of the identical side, thereby delimiting an internal cavity .…”