Incorporation of Three or Two Distal Double Bonds at the Methylene Bridges of the Calix[4]arene Scaffold

Abstract

Partial oxidation of the 1,3-alternate atropisomer of p-tert-butylcalix[4]arene tetraacetate with CrO3 afforded mainly a mixture of trioxo- and tetraoxo-calix[4]arene tetraacetate derivatives. The trioxotetrahydroxy derivative 6 was isolated from the mixture after hydrolysis of the crude product, followed by trituration with ethanol. Trioxocalix[4]arene adopts in the crystal a 1,2-alternate conformation. Acetylation or alkylation of the tetrahydroxytrioxocalix[4]arene 6 with acetic anhydride and 1-bromobutane, respectively, afforded exclusively a single atropisomer of the product, which in both cases were characterized as the 1,3-alternate form. Addition of MeLi to the tetramethyl and tetrabutyl ether of the trioxocalix[4]arenes followed by 3-fold elimination of water yielded calixarene derivatives possessing three exocyclic double bonds at the bridges. Reaction of the dioxotetramethoxy calix[4]arene 9b with MeLi followed by 2-fold elimination of water afforded calixarene 11 with a pair of distal exocyclic double bonds at the bridges. Both the tetramethyl ether derivatives 9b and 11 exist in solution as a mixture of the 1,2-alternate and 1,3-alternate conformers, but in the crystal both adopt a 1,2-alternate conformation.

Preparation and Crystal Structure of the 1,3‐alternate Atropisomer of a Calix[4]radialene

“…On these grounds, it can be concluded that in contrast to the parent 6a , the alkylation of 5 with this reagent proceeds with high stereoselectivity and affords a single atropisomeric product. A similar stereoselective butylation was recently observed in a calix[4]arene derivative possessing three oxo groups at the bridges 9b. The simplicity of the NMR pattern of the product is consistent with either a cone or an 1,3‐alternate form.…”

Calixrotanes: Calixarenes Incorporating Spiro‐Linked Cyclopropyl Groups

“…We recently described the preparation of calixradialenes, that is, calix[ n ]arenes possessing exocyclic double bonds at all the bridges (e.g., 3 , 4 ) as well as calix[4]arene derivatives possessing two or three exocyclic double bonds . A key step in the introduction of the double bonds involved the reaction of keto‐calixarenes with MeLi, followed by acid‐catalyzed dehydration of the isomeric mixture of addition products.…”

“…Calixarene 17 displays in the 1 HNMR spectrum as ignal at d = 5.41 ppm characteristic of the vinyl protons of the exocyclic double bonds in calixradialenes. [15] Calixarene 17 was treated with dichlorocarbene and the CÀ Cl bonds of the crude product were reduced with sodium in tBuOH/THF to afford the target product 18 [Eq.…”

Calix[6]arene Derivatives with Differently Modified Bridges

“…Calixarenes possessing a pair of carbonyl and bromomethylene bridges ( 4 and 5 , Scheme ) were obtained via photochemical bromination of 1a with 6.3 equivalents of NBS followed by hydrolysis of the resulting hexabromo derivatives. These compounds proved to be useful stating materials for the preparation of calix[4]arenes with two different modification of the methylene bridges . Here we describe the preparation of a larger analog of 4 , i.e., a calix[6]arene derivative possessing both a pair of distal carbonyl groups and four monobrominated bridges.…”

“…These compounds proved to be useful stating materials for the preparation of calix [4]arenes with two different modification of the methylene bridges. [12][13][14] Here we describe the preparation of a larger analog of 4, i.e., a calix [6]arene derivative possessing both a pair of distal carbonyl groups and four monobrominated bridges. Scheme 2.…”