Dehydroannulenes. I. Synthesis and Properties of 1,5,10,14-Tetramethyl-6,8,15,17-tetrakisdehydro[18]annulene

Abstract

1,6,10,15-Tetramethyl-7,9,15,17-cyclooctadecatetraene-2,4,11,13-tetrayne-1,6-diol (VII), a 18-membered cyclic glycol, was synthesized by a stepwise reaction sequence starting from 3-methyl-2-penten-4-ynal (III). Treatment of the cyclic glycol (VII) with stannous chloride dihydrate in concentrated hydrochloric acid yielded tetramethyltetrakisdehydro[18]annulene (VIII). Examination of the NMR spectra clearly indicates that the tetrakisdehydro[18]annulene (VIII) containing formal diacetylene and hexapentaene units sustains a strong diamagnetic ring current and has a high conformational stability.

Syntheses and properties of trimethyltetradehydro[15]annulenones and the benzannelated derivatives

“…spectra (see below). A similar observation is made for the annulenones (4)-( 7) and protonation, are observed in the cases of the alkylated (8)- (11) [(4) > (5) (6) > (7); (8) > (9) z (10) > annulenones (4), (€9, and (12) (50-70 nm) than in those (11); see ref.…”

“…the acyclic ketone (23) (49%) which led to the dibenzannulenone ( 11) (68%). The annulenones ( 8)- (11) thus obtained proved to have the configuration with the ccmethyl group outside the ring, by an analysis of their lH-n.m.r. spectra.…”

“…The syntheses of the annulenones ( 8)-( 15) were carried out by the same procedure as reported.lg For (8)- (11) gave the ketone (20) (69%) which was oxidized to afford the benzannulenone (9) (76%).…”

“…with increasing number of fused benzene rings on the tetradehydro[l5]annulenone system, which is in accord with the result found for the bis-(cyc1ohexene)-annelated comp~unds.~a Variable-temperature lH n.m.r. spectra of (4)-( 15) were run over the range -60 to +SO "C, the results of (10') x (13') z (14')J > (7) x (11) x (15), H7') = protons (HB, HB', HD' ) of (8) move to slightly higher field, whereas those of the outer protons ( H A , Ha, HO, HE') and three methyl protons move to slightly lower field. However, the JB,C value (11 Hz), indicating an s-trans relationship of the HB and HC bonds, does not vary from -60 to +60 "C, thus excluding a change of conformation of (8) due to rotation of the CH*=CHB double bond over this temperature range, in contrast to the case for the trime t h yltet radehydro [13] annulenone (1).…”

Tricyclic system containing large rings. The synthesis of fully-conjugated [12](1,3)[12](4,6)cyclophanpolyenepolyynes and related compounds

“…The Wittig reaction of 1,2,4,5-tetrakis(tripheny1phospho-niomethy1)benzene tetrabromide, 6 (6), and 4 molar equivalents of (22)-3-methyl-2-penten-4-ynal, 7 (7), in THF with n-BuLi at -60°C yielded only the desired all-trans isomer, 8, as crystals in 13% yield; 8 was rather unstable. Oxidative coupling of 8 was carried out with anhydrous Cu(OAc), in pyridine and ether at 50°C (8).…”