Recent Advances in the Baylis−Hillman Reaction and Applications

The past decade of organic chemistry may be charcterized as a period of violent development of new synthetic methods. This was accompained by a systematization of the analysis of synthetic problems (synthetic strategy). The planning of the synthesis of an organic target molecule is greatly facilitated by distinguishing between reagents X(C)n … with normal reactivity (acceptor properties at C1,3,5…, donor properties at X, C2,4…) and with reactivity umpolung (acceptor properties at X, C2,4…, donor properties at C1,3,5…). In this context, reactivity umpolung turned out to be useful as a heuristic principle, as a classification scheme, and as an aid for locating so-called strategic bonds (synthon, transform, and antithesis according to E. J. Corey). There are six principal methods of umpolung: 1 2n-oxidation, heteroatom exchange and modification, homologation and its reversal, the cyclopropane “trick”, use of acetylenes, and redox reactions; under certain circumstances none of these techniques is necessary in cases where direct umpolung is possible. Throughout the article, normal reactivity is indicated by green print; reactivity umpolung by red print.

Methods of Reactivity Umpolung

The electrophilic/nucleophilic character of a series of captodative (CD) ethylenes involved in polar cycloaddition reactions has been studied using DFT methods at the B3LYP/6-31G(d) level of theory. The transition state structures for the electrophilic/nucleophilic interactions of two CD ethylenes toward a nucleophilically activated ethylene, 2-methylene-1,3-dioxolane, and an electrophilically activated ethylene, 1,1-dicyanoethyelene, have been studied, and their electronic structures have been characterized using both NBO and ELF methods. Analysis of the reactivity indexes of the CD ethylenes explains the reactivity of these species. While the electrophilicity of the molecules accounts for the reactivity toward nucleophiles, it is shown that a simple index chosen for the nucleophilicity, Ν, based on the HOMO energy is useful explaining the reactivity of these CD ethylenes toward electrophiles.

Understanding the reactivity of captodative ethylenes in polar cycloaddition reactions. A theoretical study.

2. Essential Components: Earlier Developments 5449 2.1. Activated alkenes/alkynes 5450 2.1.1. Acyclic activated alkenes/ alkynes 5450 2.1.2. Cyclic activated alkenes 5451 2.2. Electrophiles 5451 2.3. Catalysts 5452 3. Essential Components: Recent Developments 5452 3.1. Activated Alkenes/Alkynes 5452 3.2. Electrophiles 5460 3.3. Catalysts 5477 4. Asymmetric Baylis-Hillman Reaction: Earlier Developments 5495

Recent contributions from the Baylis-Hillman reaction to organic chemistry.

Ynamides display an exceptionally fine balance between stability and reactivity. They also offer unique and multiple opportunities for the inclusion of nitrogen-based functionalities into organic molecules, and are emerging as especially useful and versatile building blocks for organic synthesis. Recent breakthroughs in the preparation of these substrates have revitalized interest in nitrogen-substituted alkynes, and the beginning of the 21st century has witnessed an ever-increasing number of publications reporting the development of new reactions or synthetic sequences starting from ynamides. This Review highlights major developments in this area.

Ynamides: versatile tools in organic synthesis.

http://journals.iucr.org/b/issues/1977/02/00/a14410/a14410.pdf

Phényl‐1 diméthylamino‐3 cyano‐4 amino‐5 pyrazole

Heterocyclisations of 1,4-bis-nucleophiles with the tetrahydroazepin-2-one 1 and gamma-butyrolactone 2 gave imidazolidine 9, 12, oxazolidines 3, 10, 13, 15 and thiazolidine 4 as a mixture of two diastereoisomers in various proportions. The structure and the relative configurations of these heterocycles were established by X-ray diffraction analysis and by comparison of F-19- and C-13-NMR data.

New trifluoromethylated imidazolidines, oxazolidines and thiazolidines starting from 3-(1,1-dihydroxy-2,2,2-trifluoroethyl)-1-methyl-tetrahydroazepin-2-one and alpha-(1,1-dihydroxy-2,2,2-trifluoroethyl)-gamma-butyrolactone

Use of Tert-butyl Sulfoxides As Latent Sulfenyl Cation Equivalents

beta-Trifluoracetyl-N-methyl-2-pyrrolidone undergoes once or twice the Robinson annelation with methylvinylketone. The spiro compound 6 can be trifluoroacetylated to the corresponding 1,3-diketone 8 for heterocyclizations with bis-nucleophiles. Furthermore, 6 furnishes spirocyclohexadienone 15 with potential for aromatisation.

Spiroannelation Starting From Beta-trifluoroacetylpyrrolidone

New trifluoromethylated pyrazoles 5b,c,f have been prepared by condensation of 3-trifluoroacetyl benzolactams 1a,b,c and 2 with hydrazines by opening of the lactam moiety. The structure of pyrazoles was established by X-ray diffraction analysis and by comparison of C-13-NMR data. The geometry of intermediate hydrazones 3c-e and their cyclisations were also investigated.

Synthesis of 5-hydroxy-3-trifluoromethyl-pyrazoles By Ring-opening of 3-trifluoroacetyl-benzolactams

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