Synthesis and properties of methano-[12]-, -[18]-, -[20]-, -[22]-, -[24]-annulene and dimethano-[20]- and -[24]-annulene

Annulenes, 1980–2000

“…As the temperature is lowered, the diatropic ring current increases. 137 Similarly, 1,6-methano-bridged derivatives of [20]-, [22]-and [24]annulene have been prepared, and they display similar trends. 98, 137 Conformational mobility gives rise to temperature dependent 1 H NMR spectra and, as the temperature is lowered, the ring current increases.…”

“…137 Similarly, 1,6-methano-bridged derivatives of [20]-, [22]-and [24]annulene have been prepared, and they display similar trends. 98, 137 Conformational mobility gives rise to temperature dependent 1 H NMR spectra and, as the temperature is lowered, the ring current increases. The temperature dependence is greater than in the dehydro-analogues, which will be discussed later.…”

“…The antiaromatic [4n] π-electron systems, 1,6:11,16dimethano [20]annulene 84 and 1,6:13,18-dimethano[24]annulene 85 have been prepared and are nearly atropic due to the severe deviation from planarity. 133, 137 The triply bridged system, 1,6:9,14:17,22-trimethano [24]annulene 86, is nonplanar and weakly paratropic. However, reduction with lithium metal forms a strongly diatropic 26 π-electron system, apparently with a C 3 symmetry axis.…”

Synthesis and properties of methanothia-[15]-, -[17]-, -[19]-, -[21]-, -[23]-, -[25]-, -[27]-, -[29]-annulene and dimethanodithia-[26]- and -[30]-annulene

“…Reaction of 1 -formyl-6-(2-formylvinyl)cyclohepta-1,3,5-triene (3b) and the salt (4a) afforded only a dimer, 4,9 : 17,22-bismethano-l,l4-dithia[26]annulene (15) in 2.7% yield. The reactions of the higher dicarbaldehydes (3d)--(3j) with the salt (4a) afforded the corresponding monomeric condensation products, 6,l l-methanothia [17]- (8) (1.6%), 8,13-methanothia [19] were obtained as coloured crystals and proved to be thermally unstable and sensitive to diffused light and air; in particular, compound (14) rapidly decomposed even after recrystallization from common organic solvents at low temperature.…”

The McMurry Coupling and Related Reactions

“…The ability of the McMurry reaction to form medium-and large-sized rings efficiently, while at the same time building in considerable strain is also evident in the synthesis of the betweenanene 75 [101] and the heptafulvalene 76; the latter results from a transannular carbonyl coupling reaction and was transformed into displeiadiene after dehydrogenation [102]. A variety of conjugated cyclic polyenes, such as 77 and 78 [103,104], as well as unique examples of cyclo-1,3-dien-5-ynes 79 [105], have been prepared by the intramolecular coupling of dialdehydes. The tetraene 80, which was investigated as a tetradentate ligand for transition metals, accommodates an Ag þ ion within the cavity to give a unique square-planar com- plex [106].…”