Applications of NMR Spectroscopy in Organic Chemistry.

Identification and synthesis of volatiles released by the myxobacterium Chondromyces crocatus

The oxidative conversion of alicyclic ketones into lactones with permonosulfuric acid was discovered by Baeyer and Villiger in 1899, and in their honor the general process by which ketones are converted into esters or lactones is now known as the Baeyer–Villiger reaction. The literature on this synthetically useful process has been reviewed comprehensively through 1953 in Volume 9 of Organic Reactions, and less comprehensive reviews of the reaction have appeared since then. More recent investigations have led to the development of new synthetic reagents, to improvements in experimental reaction conditions, and to a better understanding of regiochemical and stereochemical aspects of the reaction. Baeyer–Villiger reactions now often can be carried out with functional group chemoselectivity and regiochemical control. Although the recent removal from commerce of 90% hydrogen peroxide and reagents based upon this oxidant are a setback to Baeyer–Villiger reaction methodology, alternative reagents, catalysts, and methods described in this review are available to fill the gaps.



The definition of the Baeyer–Villiger reaction is somewhat fuzzy, and can be considered to include both ketones and aldehydes. In addition to the traditional use of organic and inorganic peracids as oxidants, examples of oxygen insertion reactions using hydrogen peroxide, alkyl peroxides, and several metal ion oxidants are considered to fall within the scope of this chapter and are included in the tabular survey.


Keywords:

Baeyer-Villiger oxidation;
ketones;
aldehydes;
Criegee mechanism;
migrating step;
rate determining addition;
straight chain ketones;
monocyclic ketones;
polycyclic ketones;
α,β-unsaturated ketones;
1,2 dicarbonyls;
reagents;
fused ring ketones;
peracid reactions;
α,β-unsaturated aldehydes;
ketals;
acetals;
side reactions;
alternative methods;
experimental procedures;
scope;
limitations;
spirocyclic ketones;
bridged compounds;
nitrogen derivatives

The Baeyer–Villiger Oxidation of Ketones and Aldehydes

A reconstructed karyotype of Vicia faba with all chromosomes individually distinguishable was treated with triethylene melamine (TEM), cytostasan (CYT) (a new benzimidazol nitrogen mustard), mitomycin C (MI), ethanol (EA) and X-rays. The distribution within chromosomes of induced chromatid abberations was non-random for all agents. The number of segments involved in aberration clustering corresponded to the number of sites representing constitutive heterochromatin, or the regions immediately adjacent to these, as evidenced by the position of Giemsa marker bands. Which of these potential regions of aberration clustering reacted with preferential involvement in aberrations was, in part at least, dependent upon the inducing agent used. It is argued that this may be due to differences in the base composition and/or molecular conformation of heterochromatic regions. Unexpectedly, the distribution pattern of chromatid aberrations induced by mitomycin C was found to be different from those after treatment with the alkylating agents TEM and cytostasan although mitomycin C is assumed to induce aberrations via alkylation. If mitomycin C-induced aberrations are indeed due to alkylation, this indicates that different alkylating agents do not necessarily result in identical patterns of abberation clustering. The other two alkylating agents and ethanol resulted in similar patterns of preferential distribution of abberations. X-Ray induced chromatid aberrations also showed a non-random intrachromosomal distribution, but the clustering was less pronounced than after treatment with the chemical agents.

Non-random intrachromosomal distribution of chromatid aberrations induced by X-rays, alkylating agents and ethanol in Vicia faba

The Beckmann rearrangement, the acid-mediated isomerization of oximes to amides, was discovered by Beckmann in 1886. As one of the oldest and most familiar transformations in organic chemistry, it has been reviewed several times. What has become known as the Beckmann fragmentation was in fact first observed by Wallach in 1889 but was not developed extensively until the 1960s. It has been referred to by several names over the years and has also been reviewed. The rearrangement cyclization is the intramolecular cyclization of a nitrilium ion generated by Beckmann rearrangement from an oxime. Within the context of an aromatic terminator, the process was first reported by Goldschmidt in 1895. Wallach reported the first case of an aliphatic terminator in 1901, although the reported structure was incorrect, and Perkin was apparently the first to observe a heteroatom terminator, but he also reported an incorrect structure. The process has been exploited only quite recently. This chapter is an update of these reactions, last reviewed in this series in 1960. Not covered are transformations that have been labeled Beckmann-type reactions but are mechanistically unrelated. The most prominent of these is the so-called photochemical Beckmann rearrangement, first observed by De Mayo in 1963 and discussed in a review several years ago. Worthy of mention, however, is the fact that many oximes that suffer fragmentation under acidic conditions undergo rearrangement when photolyzed.



Throughout this chapter, the (E) and (Z) nomenclature is used to describe oxime geometry.


Keywords:

Beckmann reactions;
rearrangements;
fragmentations;
cyclizations;
ketoximes;
haloimines;
nitrones;
aldoximes;
terminators;
mechanisms;
scope;
limitations;
experimental procedures;
stereochemistry

The Beckmann Reactions: Rearrangements, Elimination–Additions, Fragmentations, and Rearrangement–Cyclizations

Ring enlargements—II

Stereochemistry of grignard reactions on some conformationally mobile δ-keto esters: The effects of changing solvent and reactant

The 1H and 13C NMR chemical shift assignments of 10‐substituted decal‐2‐ones, cis (H, CH3 and CO2CH3) and trans (H, CH3, OH and CO2C2H5) were based on 2D COSY and HETCOR experiments, supported by selective spin decoupling experiments. The discrimination between the cis and the trans conformations was ruled out on the basis of the J(1a,9) magnitudes related to dihedral angles (Karplus rule) and also on the 13C shielding values of C‐4 of the cis compounds, which are much more shielded than those of the trans counterparts. The best and fastest criterion of differentiation between cis and trans conformers is the constant appearance in the 13C PND spectra of the cis series of some signals of broadened linewidth and low intensity, essentially C‐4, C‐5 and C‐7, a clue to site exchange processes; the trans counterparts showed only sharp signals because of their existence as a single conformation. Copyright © 2000 John Wiley & Sons, Ltd.

G. Di Maio

Papers

Ring enlargements—II

Stereochemistry of grignard reactions on some conformationally mobile δ-keto esters: The effects of changing solvent and reactant

Analysis of 1H and 13C NMR spectra of cis‐ and trans‐10‐substituted decal‐2‐ones by 2D NMR techniques

Ring enlargement—III

Steric and kinetic effects of changing solvent and reactant in grignard reactions: Conformationally mobile versus rigid δ-keto esters