Bredt‐Verbindungen und Bredt‐Regel

Abstract

Herrn Professor Theodor Wieland zum 60. Gehurtstag gewidmetDie Bredt-Regel[*'', in fruheren Dezennien vor allem als aussonderndes Kriterium bei Strukturzuordnungen bewahrt, wurde in den vergangenen Jahren zum Stimulans fur Bemuhungen um die Synthese gespannter bicyclischer Systeme mit einer Bruckenkopfdoppelbindung. Auf der Grundlage der in solchen Systemen wirksamen Ringspannungskrafte wird eine erweiterte Bredt-Regel diskutiert. Die von dieser Regel betroffenen ,,Bredt-Verbindungen", zu denen auch bicyclische Systeme gehoren, die bisher nicht unter diesem Aspekt gesehen wurden (z. B. uberbruckte Methylen-cyclopropane), bilden ein klar umrissenes, interessantes Feld innerhalb der Chemie hochgespannter cyclisch-ungesattigter Kohlenwasserstoffe.

The Electronic Structure of Vinyl Ethers and Sulfides with Interrupted Conjugation Examined by Photoelectron Spectroscopy

“…It agrees within the limits of error with the one observed for 1, namely I&) = 8.35 eV. This may seem surprising because 1 belongs to the class of 'anti-Bredt' hydrocarbons [20] for which one would have expected a reduced l,(n)-value, in view of the deformation which must necessarily be present in the double bond. However, it has been shown [21] …”

Total Synthesis and Olfactory Evaluation of (1R*,3S*,6S*,7S*,8S*)‐ 3‐Hydroxy‐6,8‐dimethyltricyclo[5.3.1.03,8]undecan‐2‐one: A New Synthetic Route to the Patchoulol Skeleton

“…In accordance with the results of Yamada et al, [6] the enolization of ketone 14 was expected to be completely C-3 regioselective. Applying the guidelines that Köbrich [27] established for the application of Bredt's rule, the ∆ 1,2 -system should correspond to an S = 6 [2,2,2] Bredt-forbidden olefin, while the ∆ 2,3 -enol should not be a Bredt alkene, as its ring strain would be in the order of an S = 7 [3,3,1] bicycle. In agreement with this were density-functional calculations on the B3LYP level with the 6-31G* basis set, which favored the ∆ 2,3 -enol system by as much as 159 kJ/mol (38.0 kcal/mol).…”

Methods for the Preparation of Bridgehead Olefins

“…Section 2.9). It is hardly surprising then, that adamantene itself, which is comparable with trans-cyclohexene, is not formed either by Hofmann elimination from (13) or from (16). Furthermore (14) merely rearranges to the dithiocarbonic ester (IS) under the conditions of the Tschugaeff reacti0n1~~' (cf.…”

“…Thus the dimerization formally corresponds to [n2s + n2,]-cycloaddition. It has been estimated for a strain of about 20 kcal/mol in ( I 16) that isomerization of (116) to ( 1 1 7 ) is exothermic to the extent of about 10 kcal/mol. It is to be expected that directed studies of the dimerization of reactive bridgehead olefins should lead to considerable refinement of the selection principles and mechanistic models of [2 + 21-cycloadditions.…”