Asymmetric 1,3-Dipolar Cycloaddition Reactions

The functionalization of C(sp3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area.

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Complementary Strategies for Directed C(sp3 )-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer.

Radical reactions in organic synthesis

Optically active isoxazolidines via asymmetric cycloaddition reactions of nitrones with alkenes: applications in organic synthesis

The achievement of a synthesis of a complex organic molecule involves a number of distinctly identifiable operations which, however, are not strictly independent of one another. These include the choice of the molecule to be synthesized, the development of a synthetic strategy and plan in general outline, the selection of specific individual steps and their ordering, and the experimental execution of the synthesis. The absence of a clean separation between component elements makes the task of analysing and understanding Synthesis as an intellectual discipline appear quite forbidding, especially in the most crucial aspect, derivation of a general plan. Further, the enormous diversity and number of organic structures now known to exist, the incredibly broad spectrum of reactions available for synthesis, and the uncertain and severe limits on the applicability of any given reaction all combine to create an impression that the design of a synthesis is apt to be tenuously hypothetical and is mainly a function of the unique circumstances in each particular case and, moreover, that considerations of a highly general nature are neither dominant nor very useful. None the less, a sufficiently great number and variety of syntheses have now been completed to encourage attempts at setting down in a generalized form the process by which a synthetic chemist devises an original but valid synthetic route to a complicated structure. Such an effort surely is more than an intriguing theoretical exercise; it is a prerequisite to a deeper comprehension of Synthesis and the methodologies which are fundamental to it, and it is likely to be a keystone in the rational development of Synthesis to still higher forms. For example, any technique for the automatic generation of synthetic schemes by a computer will require a complete and detailed definition of the elements of Synthesis and their mutual interaction, in a most general sense.

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General methods for the construction of complex molecules

Treatment of 3β-acetoxy-20β-hydroxy-5α-pregnane (11) with lead tetraacetate in benzene allows the selective introduction of an oxygen function at the no11 activated angular methyl group C-18. The main product of this reaction is the 18,20β-oxido compound I11 as proved by its conversion into the lactone V and the lactol VI.

Über Steroide und Sexualhormone. 211. Mitteilung. Direkte Einführung einer Sauerstoffunktion in die Methylgruppe C-18 im intakten Steroidgerüst

Configuration and reactivity of ten-membered 5,10-seco-compounds obtained by fragmentation of 5-hydroxy-steroids

Results previously reported on the fragmentation of monohydric alcohols with lead tetraacetate are extended and correlated on the basis of new experimental evidence.

Über Steroide und Sexualhormone 227. Mitteilung. Die Fragmentierung einwertiger Alkohole mit Blei(IV)-acetat

Lead tetraacetate oxidation of saturated aliphatic alcohols.—III

The influence of the environment of the hydroxyl group on the course of the oxidation of 20-hydroxy-steroids with lead tetraacetate has been investigated. It could be shown that, whenever the normal reaction — ether formation between C-18 and C-20 — is inhibited by steric factors, fragmentation processes occur, resulting in the formation of 17α-acetoxy compounds and of saturated ring D unsubstituted compounds respectively.

M. Lj. Mihailovic

Papers

Über Steroide und Sexualhormone. 211. Mitteilung. Direkte Einführung einer Sauerstoffunktion in die Methylgruppe C-18 im intakten Steroidgerüst

Configuration and reactivity of ten-membered 5,10-seco-compounds obtained by fragmentation of 5-hydroxy-steroids

Über Steroide und Sexualhormone 227. Mitteilung. Die Fragmentierung einwertiger Alkohole mit Blei(IV)-acetat

Lead tetraacetate oxidation of saturated aliphatic alcohols.—III

Über Steroide und Sexualhormone. 221. Mitteilung. Weitere Oxydationsversuche von 20-Hydroxysteroiden mit Blei(IV)-acetat