The quest for planarizing distortions in hydrocarbons: two stereoisomeric [4.5.5.5]fenestranes

Synthesis and reactions of two stereoisomeric [4.5.5.5]fenestranes with bridgehead substituents

“…Derivatives of triquinane possibly formed from the tertiary carbenium ion at C(12) via 1,2 rearrangement from C(7) are not observed. 1 It is apparent that the attempted dehydration in the cis,trans,cis,cis-[4.5.5.5]fenestranol 15 leads to a release rather than built up of strain. According to our semiempirical calculations 15 is more strained than 12 by almost 20 kcal/mol.…”

“…The rearrangement to the triquinane structure was not observed. 1 Despite of extensive experimental efforts no fenestrane has hitherto been observed with opposite bond angles both larger than 130 .…”

“…6 Semiempirical, DFT calculations and X-ray analyses of some fenestranes prepared clearly show, that two opposite bond angles across the quaternary carbon are larger than 109.4 . 1 As mentioned earlier, ring contraction, inversion at the bridgehead C atoms, bridgehead double bonds and alkyl substituents at the peripheral bridgehead C centres have been identified as those parameters, which enhance the opening of two opposite bond angles in the central C(C) 4 moiety. 7 …”

“…IR: 1730vs, 1450m, 1375m, 1300m, 1285m, 1180s, 895m. 1 Freshly distilled 4 (28.44 g, 0.2 mol) was shaken with NaOEt (freshly prepared from Na and an equimolar amount of abs EtOH by reflux in abs Et 2 O for 16 h under Ar, removal of the solvent and drying at HV) under Ar until a half solid yellow gel had formed. In partial vacuo (600 mm) the mixture was heated to 120 C to give a liquid suspension.…”

“…1 The preparation of natural products and the creative development of methods by which such structures are formed in a few steps find continuous attention. 2e5 In addition, fenestranes of interest for the study of planarizing distortions in C(C) 4 substructures, forming the central part in fenestranes.…”