An improved preparation of vinyl iodides

The Bredt rule, which proved useful in earlier decades mainly as an exclusion criterion in the assignment of structures, has in recent years become the stimulus for efforts to synthesize strained bicyclic systems with a bridgehead double bond. On the basis of the ring-strain forces operating in such systems, an extended Bredt rule is discussed. The “Bredt comgounds” to which this rule applies, which include bicyclic systems not prevoously consodered from this point of view (e.g. bridged methylenecyclopropanes), form a clearly circumscribed, interesting field within the chemistry of highly-strained hydrocarbons with ring unsaturation.

Bredt Compounds and the Bredt Rule

Alkene synthesis via .beta.-functionalized organosilicon compounds

Die Bredt-Regel11 , in fruheren Dezennien vor allem als aussonderndes Kriterium bei Srukturzuordnungen 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.

Bredt-Verbindungen und Bredt-Regel†

Publisher Summary This chapter focuses on stereochemical approaches to mechanisms of hydrocarbon reactions on metal catalysts. The chapter discusses the classic Horiuti–Polanyi mechanism of hydrogenation of olefins and describes competitive reactions for hydrogenation of cycloalkenes. Some basic facts are established from exchange with deuterium of numerous alkanes and polycycloalkanes especially on Pd catalysts. The interconversion of monoadsorbed and αβ-diadsorbed species can be very rapid especially on Pd and Rh before desorption of alkane. This interconversion is referred to as the “αβ process.” The αβ process propagates readily along a chain of carbon atoms, and, in acyclic paraffins with rapid rotation about C–C bonds, every H atom is readily replaced, as evidenced by the very large quantities of the perdeutero isomer in initial products from exchange of n-hexane on Pd films. The propagation of the exchange reaction is blocked if the chain of carbon atoms contains a quaternary center or a bridgehead.

Stereochemical Approaches to Mechanisms of Hydrocarbon Reactions on Metal Catalysts

Concerning the Existence of 1‐Norbornene

Does 1‐Norbornene Exist?

Zur frage nach der existenz von 1‐norbornen

Existiert 1‐Norbornen?

1,2 exo-Diiodo-norbornane (4) was prepared from norcamphor hydrazone by oxidative iodination and subsequent rearrangement of the 2,2-diiodo-bicyclo [2.2.1]heptane (2). The stable α-iodohydrazone 11 was obtained from 1-iodo-bicyclo[2.2.1]heptan-2-one (10), which itself was prepared from 1-iodo-norbornene (5). Subsequent treatment of 11 with iodine lead to 1,2,2-triiodo-norbornane (12) and l,2-diiodo-norborn-2-ene (13). 1,2 endo-Diiodo-norbornane (14) was obtained by stereoselective reduction of 12 with tribtityltinhydride or by reaction of 13 with diimide.

Ernst‐Peter Krebs

Papers

Concerning the Existence of 1‐Norbornene

Does 1‐Norbornene Exist?

Zur frage nach der existenz von 1‐norbornen

Existiert 1‐Norbornen?

Preparation of 1,2exo‐ and 1,2endo‐Diiodo‐bicyclo[2.2.1]heptane