F. Krollpfeiffer

Bio: F. Krollpfeiffer is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 25 citations.

3.3 – The Intramolecular Aromatic Friedel–Crafts Reaction

Abstract: Most of the general features of the intermolecular Friedel–Crafts acylations that are the subject of Volume 2, Chapter 3.2 also apply to the intramolecular versions. The present chapter should be regarded as an extension to the earlier one. The intramolecular Friedel–Crafts reaction has been reviewed previously,1 including reactions specifically involving the use of polyphosphoric acid.1c We will concentrate our attention on more recent examples in order to exemplify the general principles that were also described in those reviews. There is no reason to suppose that the mechanistic considerations that we considered in the earlier chapter do not also apply in the present case. The thermodynamic problems associated with intermolecular reactions result in some important changes to those general features when we consider the intramolecular versions. The enthalpy effect relates to any ring or steric strain that may be present in the transition state leading to cyclization and the entropy effect relates to the ease or difficulty of making the two ends of the reacting system meet. As is the case with the majority of nonradical cyclization reactions, six-membered rings are formed most easily, followed by five- and seven-membered systems. Medium-sized rings are not easily obtained2 and large-sized rings are only obtained in reasonable yields using high dilution techniques. Thus the conversion of 6-phenylhexanoic acid into the acid chloride and cyclization using aluminum chloride in dichloromethane gave the benzocyclooctenone in only 38% yield (equation 1).2b Other reactions leading to the formation of, for example, an eightmembered heterocyclic ring (a benzazocinone),2c have also been reported using a procedure2d that involves the use of 3 equiv. of aluminum chloride. A reaction of 16-phenylhexadecanoyl chloride with aluminum bromide gave the 20-membered ring product shown in equation (2) in 70% yield using a high dilution procedure.3 In analogous reactions leading to the formation of 18-, 15- and 13-membered rings the products were obtained in 57%, 30% and 5% yields respectively. Rather surprisingly the cyclization of o-β-phenethylphenylacetic acid using polyphosphoric acid gave 2,3,6,7-dibenzocyclooctanone in 93% yield.4 Presumably this results from the presence of the four sp3 carbon atoms, which impart significant rigidity to the molecule and hence increase the chance that the two ends of the reacting system will meet. We will classify the remaining parts of this chapter according to the size of ring produced.

Thia-Aromaten, II. 1- und 2-Thia-naphthaliniumsalze

Abstract: Die unsubstituierten Grundkorper der Benzo-thiopyryliumverbindungen, das 1- und das 2-Thia-naphthaliniumperchlorat sowie das 6.7-Dimethoxy-1-thia-naphthaliniumperchlorat werden auf mehreren Wegen erstmalig dargestellt, ihre chemischen Eigenschaften beschrieben, die Absorptionsspektren diskutiert.