The Boat Form in Six-Membered Rings.

Dimerization of Pyramidalized 3,4,8,9‐Tetramethyltetracyclo [4.4.0.03,9.04,8]dec‐1(6)‐ene to a Hydrocarbon Featuring Four Cyclohexane Rings in Boat Conformations

“…Finally, in spite of the three cyclobutane rings, and in sharp contrast with the behavior of previously described dimers of highly pyramidalized alkenes, the nonacycle 7 is thermally stable. 10,13 .0 1,10 .0 3,8 .0 14,17 ]nonadec-3,5,7-triene (5). A solution of tert-butyllithium (1.6 m in pentane, 0.61 mL, 0.97 mmol) was slowly added, under stirring, to a cold (À67 8C) solution of 3 (252 mg, 0.6 mmol) and 1,3-diphenylisobenzofuran (186 mg, 0.68 mmol) in anhydrous THF (10 mL).…”

“…182-183 8C. (8). Finely cut sodium (0.49 g, 21.5 mmol) was added to boiling anhydrous 1,4dioxane (25 mL) and the mixture was heated with stirring under an argon atmosphere until the metal melted.…”

“…The diiodo compound 3 was obtained in 27 % yield by using a iododecarboxylation procedure recently reported by Gandelman and co-workers. [8] Previous attempts to carry out the iododecarboxylation of 2 using iodosobenzene diacetate or lead tetraacetate gave even lower yields of 3. Reaction of 3 with tert-butyllithium in THF at À67 8C in the presence of 1,3-diphenylisobenzofuran furnished the expected Diels-Alder adduct 5 in 37 % yield.…”

“…Finally, the structure features four cyclohexane rings in a boat conformation. Although there are several precedents of cyclohexane rings in boat conformations, [10] most of the known examples lack the typical H-H flagpole interaction of the boat conformation (e.g. camphor and other norbornane derivatives).…”

A ring conformation of androstan-3-one

“…Similarly, a switch of carbon to oxygen in the B-ring results in a subtle conformational change of the tetracyclic ring structure [17]. Despite the boat form of the rings of the steroid molecule being less stable, this conformation of the B-ring can also be realised [18]. Deviation from typical chair conformation is also possible for the steroid C-ring that can have a twist-boat conformation [19].…”