There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

8.4.5. Nitromercuration Reactions 3878 9. Hydroamination of Alkenes and Alkynes under Microwave Irradiation 3878 * To whom correspondence should be addressed. Phone: +49 241 8

Hydroamination: direct addition of amines to alkenes and alkynes.

Asymmetric 1,3-Dipolar Cycloaddition Reactions

The Diels-Alder reaction has both enabled and shaped the art and science of total synthesis over the last few decades to an extent which, arguably, has yet to be eclipsed by any other transformation in the current synthetic repertoire. With myriad applications of this magnificent pericyclic reaction, often as a crucial element in elegant and programmed cascade sequences facilitating complex molecule construction, the Diels-Alder cycloaddition has afforded numerous and unparalleled solutions to a diverse range of synthetic puzzles provided by nature in the form of natural products. In celebration of the 100th anniversary of Alder's birth, selected examples of the awesome power of the reaction he helped to discover are discussed in this review in the context of total synthesis to illustrate its overall versatility and underscore its vast potential which has yet to be fully realized.

https://www.ch.ic.ac.uk/local/organic/pericyclic/DA.pdf

The Diels--Alder reaction in total synthesis.

http://aether.cmi.ua.ac.be/artikels/Artikels%20Gitte/Artikels/Reviews/Trans.%20Metal.%20catal.%20reactions%20Chem.%20rev.%20042127.pdf

Transition-Metal-Catalyzed Reactions in Heterocyclic Synthesis

Synopsis: With the addition of titanium tetrachloride, silyl enol ethers can react with either aldehydes or ketones forming crossed aldol products. The carbonyl group of the aldehyde or ketone is activated by titanium tetrachloride, allowing for nucleophilic attack by a silyl enol ether at the carbonyl carbon (a titanium chelate forms as an intermediate). This addition reaction is dependent upon the metal salt, solvent, and temperature used. Critique: The fact that various reaction conditions were studied to find optimal reaction conditions that gave the highest yield of cross-aldol addition products strengthened the findings in this paper. Mukaiyama and coworkers concluded first that titanium chloride was best for this reaction compared to boron trifluoride etherate and stannic chloride. Secondly, it was observed that methylene chloride gave cross-aldol products in good yield while no reaction was observed in both diethyl ether and THF. Finally, reaction with aldehydes is favored at -78 o C while ketone reaction is favored at room temperature. It was also interesting to see that the use of unsymmetric ketones allows for regiospecific addition reactions at the olefinic position on the silyl enol ether.

New cross-aldol reactions. Reactions of silyl enol ethers with carbonyl compounds activated by titanium tetrachloride

In the presence of TiCl4, trimethylsilyl enol ethers of ketones react smoothly with ketones or aldehydes at room temperature to give the aldol type addition products, β-hydroxyketones, in good yields.

New aldol type reaction

Le catalyseur chiral est genere a partir de TiCl 2 (i-PrO) 2 et du (methyl-2 phenyl-2, α,α,α',α'-tetraphenyl) dioxolanne-1,3 dimethanol-4,5,chiral

Asymmetric Diels-Alder Reaction Catalyzed by a Chiral Titanium Reagent

In the presence of certain Lewis acids, alkenes containing an alkylthio group (for example, ketene dithioacetals, alkenyl sulfides, alkynyl sulfides, and allenyl sulfades) react with electron defficient olefins to give the corresponding cyclobutene, or methylene cyclobutane derivatives. By employing a chiral titanium catalyst generated in situ from dichlorodiisopropoxytitanium and a tartrate-derived chiral diol, the [2+2] cycloaddition reaction proceeds with high enantioselectivity

Koichi Narasaka

Papers

New cross-aldol reactions. Reactions of silyl enol ethers with carbonyl compounds activated by titanium tetrachloride

New cross-aldol reactions. Reactions of silyl enol ethers with carbonyl compounds activated by titanium tetrachloride

New aldol type reaction

Asymmetric Diels-Alder Reaction Catalyzed by a Chiral Titanium Reagent

Asymmetric [2 + 2] cycloaddition reaction catalyzed by a chiral titanium reagent