Deep molecular baskets : convergent syntheses of calix[4]naphthalenes via directed ortho metallation and Suzuki-Miyaura coupling reactions

Chowdhury, Sultan (2001) Deep molecular baskets : convergent syntheses of calix[4]naphthalenes via directed ortho metallation and Suzuki-Miyaura coupling reactions. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Calix[4]naphthalenes are a new class of compounds which are analogous to the better-known calix[4]arenes, but have deeper cavities. These compounds, especially the endo calix[4]naphthalenes e.g., 31 can behave as "molecular baskets" in their abilities to complex with neutral guest molecules such as [60]fullerene. This thesis describes the synthesis of such deep molecular baskets. -- Calix[4]naphthalene (31 ) was synthesized by self-condensation reactions of 6-tert -butyl-3-(hydroxymethyl)-2-naphthol ( 29 ). Various Lewis acids were evaluated in order to obtain 31 in higher yield. Conformational properties of 31 were studied by VT⁻¹ H NMR experiments in two different deuterated solvents. Alkyl ether derivatives (41a-41b ) of 31 , and also tert -butylcalix[4]naphthalene-1,3-crown 42 were synthesized, and all compounds were shown by NMR experiments to exist in cone conformations. -- A synthetic route toward the synthesis of the C₂ᵥ -symmetrical "C-12" endo calix[4]naphthalenes e.g., 35 allowed us to evaluate the efficiency of the Suzuki-Miyaura coupling reactions for various benzylic halides and bromomethylnaphthalenes with phenyl- and naphthylboronic acids. Directed ortho Metallation (DoM) reactions using both n -butyl- and tert -butyllithium were evaluated for the introduction of various functional groups orthoto the hydroxyl group of 2-naphthol, bis(2-hydroxy-1-naphthyl)methane and their derivatives. -- Synthesis of calix[4]naphthalene (35 ) was achieved using both acid- and base-induced condensation reactions of compound 98 and aqueous formaldehyde solution. Various alkyl ether derivatives ( 113a-113d ) of 35 were obtained, and their conformational properties were studied by NMR experiments. The X-ray crystal structure of113d revealed that it exists in a cone conformation as a clathrate containing two molecules of toluene located in its hydrophobic cavity. -- Calix[4]naphthalene (114 ), an example of an endo/exo -type calixnaphthalene was synthesized using "2 + 2" Böhmer condensation conditions. Considerable effort was expended to synthesize endo calix[4]naphthalenes (78-80 ), and other calixarenes containing mixed benzene and naphthalene units (e.g., 116 ) via "2 + 2" and/or "3 + 1" Böhmer conditions. Other unsuccessful attempts were made to synthesize all the possible isomers of endo calix[4]naphthalenes (35a-c and 107 ) using Suzuki-Miyaura coupling reactions. -- Several approaches towards modifying the lower rim of calixarenes were undertaken in order to deepen their cavities. The hydroxyl groups of 2 were derivatived to triflates 118-121 and also to nonaflate 125 in order to evaluate Suzuki Miyaura, Stille and Pd-catalyzed carbonylative reaction conditions. The first successful syntheses aryl ether derivatives (131-134 and 137-143 ) of 2 were achieved using either Nucleophilic Aromatic Substitution (SN Ar) or Ullmann ether conditions.

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