Bicyclofulvene, IX. Stereoelektronische Effekte bei der Addition an 8‐Methylentricyclo[3.2.0 ^2,4 ]octan‐Derivate

Abstract

Das Aziridin-Derivat 9 wird bei der Dichlorcarben-Addition, der Hydroborierung und der Hydrierung etwas mehr von der syn-als von der anti-Seite her angegriffen. Wahrend bei 9 keine nennenswerte Wechselwirkung zwischen Dreiring und semicyclischer Doppelbindung besteht, laBt sich eine deutliche Orbital-Wechselwirkung bei den Cyclopropan-Derivaten 6 und 7 nachweisen. Dies wird mit einem bevorzugten anti-Angriff der genannten Reagenzien auf die Doppelbindung in 6 und 7 in Zusammenhang gebracht. Bicyclofulvenes, IX Stereoelectronic Effects in Additions to 8-Methylenetricycl0[3.2.1.O~~~]octane DerivativesAddition of dichlorocarbene to the double bond of the aziridine derivative 9 as well as hydroboration or hydrogenation proceed with a slight syn preference. Whereas 9 lacks significant interaction between the three-membered ring and the semicyclic double bond, interaction is marked in the cyclopropane derivatives 6 and 7. This is considered to cause the preferred anti-attack by the above mentioned reagents.Oberseite und Unterseite einer Doppelbindung sind nur bei solchen Olefinen gleich, in denen die Ebene der Doppelbindung eine Symmetrieebene des Molekiils ist, wie z. B. bei 1. Bei anderen Olefinen kann die Storung, die zu einer Ungleichheit der Ober-und Unterseite fiihrt, sterische und elektronische Ursachen haben: So liegt z. B. in 2') eine einseitige elektronische und sterische Wechselwirkung vor.DaL3 die Doppelbindung in 2 von Elektrophilen anti zum Aryl-Rest angegriffen wird, ergibt sich damit allein schon aus sterischen Griinden. Um den EinfluD elektro-

Inductive and Resonance Effects of Substituents on π-Face Selection

“…Since the oxirane and aziridine C−C bonds have also been shown to be powerful anchimeric-assistance donors in this system, the same should be true for 3-aza- and 3-oxa-8-methylene- endo -tricyclo(3.2.1.0 2,4 )octanes . The available evidence is consistent with this expectation, Scheme 55 …”

Orbital-Controlled Stereoselections in Sterically Unbiased Cyclic Systems

“…This preference is in sharp contrast to the anti preference of 41a (syn:anti = 12:88), observed under similar dihydroxylation conditions with osmium tetroxide in pyridine. While the facial selectivity of 41a has been examined previously, − that of 40a has been little studied and the topology-dependent behavior described here has not previously been documented or characterized.

…”

“…A cyclopropyl group is known to act as a strong π donor due to a high-lying occupied Walsh orbital, which is frequently regarded as an equivalent of a double bond. ,− Photoelectron spectra of the olefins 40a and 41a were previously measured and the signals assigned. ,− Vertical ionization potentials of the olefin π orbitals of 40a and 41a were found to be higher than those of the unsubstituted parent bicyclo[2.2.2]octene 35a (R 1 = R 2 = H) and 7-methylenenorbornane 28a (R 1 = R 2 = H), respectively, indicating a sizable interaction of the π orbital of the double bond with the occupied Walsh orbital of the fused cyclopropane ring. The previous account of the observed anti facial preference of 41a was based on this interaction, in particular, out-of-phase interaction of the relevant orbitals ( 4.36 ). − However, the corresponding out-of-phase interaction of the olefinic π orbital with the Walsh orbital of the cyclopropyl group ( 4.35 ) does not seem to be relevant to 40a because of the observed reverse syn preference. This view is consistent with the following observation.…”

Electronic Control of Facial Selection in Additions to Sterically Unbiased Ketones and Olefins

“…Studies of face selectivity should therefore begin with a thorough characterization of the ground-state geometry. A fine example of such analysis is provided by the study of Hoffmann and co-workers. , To interpret the syn-face selectivity in electrophilic additions 33 to a methylenenorbornane derivative, 4 , with an endo-fused aziridine ring, the X-ray structure of the substrate was determined. Besides reporting the usual bond lengths, angles, and torsion angles, the authors specifically examined 34 interplanar angles of direct relevance to face selection.…”