Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.

Photochemical reactions as key steps in natural product synthesis

Soluble Lanthanide Salts (LnCl3⋅2 LiCl) for the Improved Addition of Organomagnesium Reagents to Carbonyl Compounds

New Mechanistic and Synthetic Aspects of Singlet Oxygen Chemistry

Alkyl and aryl phosphites and phosphines react with compounds having weak heteroatom–heteroatom bonds, such as SS, OO, etc., and with azo compounds to form reactive phosphonium salts. These phosphonium salts in turn promote “redox” condensation reactions with compounds having active hydrogens. The condensation reaction of alcohols using the redox couple of a triaryl- or trialkylphosphine and a dialkyl azodicarboxylate has become known as the Mitsunobu reaction, based on his pioneering work in the late 1960s. The overall reaction is summarized, wherein the alcohol (R1OH) and acidic compound (H–Nu) are condensed to form product (R1–Nu), while triphenylphosphine is oxidized to triphenylphosphine oxide and the azodicarboxylate is reduced to the hydrazine. Although the typical redox combination is diethyl azodicarboxylate (DEAD) and triphenylphosphine, many other combinations have found selected use. The reaction is generally limited to primary and secondary alcohols, although tertiary alcohols react in a few intramolecular and intermolecular reactions. For secondary alcohols the reaction usually proceeds with clean inversion of stereochemistry. The acidic component of the reaction generally has an aqueous pKa < 15, with intramolecular reactions providing the exceptions. Examples of H–Nu include oxygen nucleophiles such as carboxylic acids and phenols; nitrogen nucleophiles such as imides, hydroxamates, and heterocycles; sulfur nucleophiles such as thiols and thioamides; and carbon nucleophiles such as β-ketoesters.



Major reviews of the Mitsunobu reaction were published in 1981 by Mitsunobu and in 1983 by Castro. The former review concentrated on reactions using DEAD/triphenylphosphine, while the latter review focused on reactions in which halogens replaced the hydroxy group using reagents such as triphenylphosphine/carbon tetrachloride, triphenyl phosphite/iodomethane, and triphenylphosphine/N-halosuccinimide. Reactions involving the DEAD/triphenylphosphine redox system are the principal subject of this chapter, with emphasis on the literature between 1981 and 1988.


Keywords:

Mitsunobu reaction;
adduct formation;
alcohol activation;
SN2 reaction;
mechanisms;
carbon–oxygen bond;
carbon–nitrogen bond;
carbon–sulfur bond;
carbon–halogen bond;
carbon–carbon bond;
ambident nucleophiles;
dehydration;
alkenes;
method comparison;
ester formation;
lactone formation;
akyl aryl ether;
epoxides;
dialkyl ethers;
enol ethers;
dialkyl ethers;
imides;
azides;
experimental procedures;
scope;
limitations

The Mitsunobu Reaction

Data on the use of sulfones and sulfoxides in total stereo-, regio- and enantioselective syntheses of natural compounds published over the last 15–20 years are discussed and classified into the most important types of reactions. The bibliography includes 420 references.

http://iopscience.iop.org/article/10.1070/RC1996v065n02ABEH000204/pdf

Sulfones and sulfoxides in the total synthesis of biologically active natural compounds

A Convenient Method for Determining the Concentration of Grignard Reagents

Diastereoselective π-facially controlled nucleophilic additions of chiral vinylorganometallics to chiral β,γ-unsaturated ketones. 2. A practical method for stereocontrolled elaboration of the decahydro--indacene subunit of ikarugamycin

Ho-Shen Lin

Papers

A Convenient Method for Determining the Concentration of Grignard Reagents

Diastereoselective π-facially controlled nucleophilic additions of chiral vinylorganometallics to chiral β,γ-unsaturated ketones. 2. A practical method for stereocontrolled elaboration of the decahydro--indacene subunit of ikarugamycin

Preparation and X-ray crystal structure analysis of a stable trimethylsilyloxy epoxide

Total synthesis of (±)-sterpuric acid

Stereochemical Course of Singlet Oxygenation of a Stereoisomeric Pair of 1,9a-Epoxydecahydro-4a,5,8a-Trimethyl-2(3H)-Anthracenones