Current Organic Chemistry, Volume 6, No. 11, 2002
The
Scope and Future of Traceless Synthesis in Organic Chemistry Pp. 937-964
Phoon,
C. W. and Sim, M. M.
Reactions
of Hydrazones with Lead Tetraacetate in Organic Synthesis Pp. 965-985
Antigoni
Kotali
Novel
Developments in Biocatalytic Organic Chemistry Pp. 987-1014
Martin
Bertau
Discovery
and Development of Cyclobutanone-Based Free Radical Ring Expansion and
Annulation Reactions Pp. 1015-1029
Wei
Zhang
Abstracts
[Back to top] The
Scope and Future of Traceless Synthesis in Organic Chemistry
Phoon,
C. W. and Sim, M. M.
Solid-phase organic synthesis has attracted considerable attention from the academic and industrial laboratories throughout the world in the last two decades. From peptides, to heterocycles, and then to the highly complex natural product combinatorial libraries, solid-phase organic synthesis has proven to be one of the most important fields in organic chemistry. One of the areas of exploding research is the use of traceless linkers to generate compounds which do not contain the undesired functional groups normally derived from the solid support.
This review summarizes the
solid-phase organic reactions published in the literatures and focuses
primarily on those utilizing cleavage via traceless linkers or chemical
reactions. The general routes to traceless cleavage include:
[1] Electrophile- or
Nucleophile-Induced Cleavage
[2] Electrophile- or
Nucleophile-Induced Cleavage with Modifications in Solution
[3] Cyclorelease via
Intramolecular Nucleophilic Attack
[4] Metal-Mediated
Cyclorelease
[5] Activated Cleavage
through Acylation
[6] Cleavage via
Cycloaddition or Cycloreversion
[7] Reductive, Oxidative
or Radical Cleavage
[8] Photolytic
Cleavage
[9] Dissociation of
Metal Complexes
The review also describes our continual
effort in the generation of cheaper and better traceless linkers, and
combinatorial libraries with biological interest.
[Back to top] Reactions of Hydrazones with
Lead Tetraacetate in Organic Synthesis
Antigoni
Kotali
The progress that has been made in organic
synthesis via the reactions of hydrazones with lead tetraacetate, mainly since
1970, is presented in this review. Thus, the synthesis of various compounds, as
gem-azoacetates, azo and diazo compounds, acylhydrazines, alkenes,
oxadiazolines, triazoles, pyrazoles, indazoles and dibenzazepinones will be
discussed. Special emphasis is given in a synthetically useful new
rearrangement that takes place in LTA oxidations of N-acylhydrazones of
ohydroxyaryl ketones and leads to high yield synthesis of 1,2-diacylbenzenes,
oacylarylcarboxylic esters, o-acylbenzoyl bromides, 1,2,3- triacylbenzenes, 1,2,3,4-
tetraacylbenzenes, o-acylbenzaldehydes and o-phthalaldehyde. Finally, some of
the applications of hydrazones and their derivatives are discussed.
[Back to top] Novel Developments in
Biocatalytic Organic Chemistry
Martin
Bertau
In the last decade, modern synthetic
organic chemistry has experienced an enormous progress in biocatalytic
methodologies. Enzymatic routes and microbial whole-cell bioconversions have
become a generally accepted synthetic tool. Recent advances in biocatalytic
chemistry focus on unconventional non-protein biocatalysts such as
catalytically active RNA-molecules, and biotransformations in ionic liquids.
The example of ethyl 4- chloroacetoacetate depicts how whole-cell biocatalysis
is developing from rather empirical screening studies towards a technology
which selectively elucidates, engineers and employs living cells for
bioconversions. This review further discusses the question whether there are
natural Diels-Alderases, and gives an overview of novel and unconventional
approaches in biodehalogenations and contrathermodynamic reactions. The
biotechnological production of hydroquinone demonstrates that the efficiency of
biocatalytic routes is not limited to stereoselective synthesis.
[Back to top] Discovery and Development of
Cyclobutanone-Based Free Radical Ring Expansion and Annulation Reactions
Wei
Zhang
This article describes the discovery and
recent progresses of cyclobutanonebased free radical ring expansion and annulation
reactions. Mechanisms associated with these reaction processes are also
discussed. Ring expansion reactions rely on selective b- scission of alkoxy
radicals generated from the cyclization of carbon radicals onto carbonyls.
Exo-substituted cyclobutanones are employed to construct cis-fused seven- and
eight-membered rings, spiro-annulated medium rings, large rings, and
cyclopropanecontaining compounds. Endo-substituted cyclobutanones can undergo
tandem rearrangements to produce bridged rings. The cyclization of
dichlorocyclobutanones followed by TMSI-induced ring opening is another ring
expansion strategy for the construction of some novel ring systems.
Cyclobutanones used for free radical reactions are readily prepared by
well-established [2 + 2] cycloadditions of ketenes with various olefins.