Preparation of Congested Thiophenes Carrying Bulky Substituents on the 3- and 4-Positions and Their Conversion to the Benzene Derivatives

Abstract

Highly congested thiophenes, 3,4-di-tert-butyl-, 3,4-di(1-adamantyl)-, 3,4-dineopentyl-, and 3-(1-adamantyl)-4-tert-butylthiophenes (4a−d), were prepared in satisfactory overall yields by intramolecular reductive coupling of 3-thiapentane-1,5-diones (1a−d) followed by acid-catalyzed dehydration of the resulting thiolane-3,4-diols (2a−d). Experimental procedures of this thiophene synthesis are fully described. Oxidation of the thiophenes 4a−d with m-CPBA gave the corresponding thiophene 1,1-dioxides 13a−d in good yields. The Diels−Alder reactions of 13a−d with phenyl vinyl sulfone gave o-di-tert-butyl-, o-di(1-adamantyl)-, o-dineopentyl-, and o-(1-adamantyl)-tert-butylbenzenes (17a−d) directly in high yields with loss of benzenesulfinic acid and sulfur dioxide. The dioxides 13a−d also underwent Diels−Alder reactions with alkynic dienophiles to give the corresponding benzene derivatives carrying two bulky substituents on adjacent positions. Pyridazines 25b,c, carrying bulky substituents on the 4- and 5-positions, were also synthesized through Diels−Alder reaction of 13b,c with PTAD. Dimethylation of the 2- and 5-positions of 13a−d was attained by treatment with strong bases followed by reactions with methyl iodide. The resulting tetrasubstituted thiophene 1,1-dioxides 14a−d reacted with DMAD to give highly congested hexasubstituted benzene derivatives 15a−d in good yields. Finally, structural features of the congested molecules are discussed on the basis of NMR analyses. Typically, the barriers to rotation (ΔH ⧧) about the benzene to the bulky substituents of 15a,c,d were determined to be 8.59, 15.3, and 7.40 kcal/mol, respectively, by NMR total line-shape analysis.

Structures and properties of two diastereomeric cyclic sulfites derived from cis‐3,4‐di‐tert‐butylthiolane‐3,4‐diol and thionyl chloride

“…After the addition, the mixture was stirred for 24 h at room temperature. The resulting Et 3 N·HCl was removed by filtration and the filtrate was washed with aqueous NaHCO 3 and water, dried over anhydrous MgSO 4 , and evaporated. The residue was chromatographed on a column of silica gel (20 g).…”

“…To our knowledge, however, syntheses of such cyclic sulfites have been rather limited [3a-d,g-h]. Herein we report the preparation of a five-membered cyclic sulfite, cis-4,5-di-tert-butyl- [4,5]-(2 -thiacyclopenta)-1,3,2-dioxathiolane 2-oxide (2), by condensation of cis-3,4-di-tert-butylthiolane-3,4-diol (1) [4] with thionyl chloride and the isolation of its two diastereomers 2a and 2b. Structures of 2a and 2b are discussed based on X-ray crystallographic analyses, spectral data ( 1 H and 13 C NMR, IR, and Raman), and DFT calculations.…”

Synthesis of substituted phthalonitrile building blocks for the preparation of non-aggregating phthalocyanines

“…After that, intramolecular reductive coupling was carried out using low-valent titanium reagent prepared from titanium(IV) chloride and zinc powder in THF at -10 o C to give the 3,4-diterc-butyl-cis-thiolane (4) (76% yield). 4 Aromatization was performed using (PTSA) furnishing 5 in 19% yield.…”

SO2‐Extrusion of an 8‐thiabicylo[3.2.1]octa‐2,6‐diene 8,8‐dioxide and rearrangement of the resulting cycloheptatriene

“…We then examined the reaction of 3,4-di-tert-butylthiophene 1,1-dioxide (5) [2] with tetrachlorocyclopropene (6) with the expectation of obtaining a cycloheptatriene 7, which would serve as the precursor that leads to a range of seven-membered nonbenzenoids possessing two tert-butyl groups at vicinal positions. Disappointingly, however, 5 failed to react with 6 probably due to the steric hindrance of 5; under forcing conditions (190 • C in a sealed tube), considerable decomposition of 6 took place.…”