A free-radical cyclization of .alpha.-bromo acetals leading to tetracyclic 9.beta.-picrasanes
About: This article is published in Journal of Organic Chemistry.The article was published on 1988-01-01. It has received 22 citations till now. The article focuses on the topics: Radical cyclization.
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TL;DR: In this article, an antibody that is remarkable in that it catalyzes both steps of an important synthetic transformation, the Rob-inson annulation, is reported, which accomplishes,in net terms, the conversion of a f c occupies a key role in organic synthesis.
Abstract: The Skaggs Institute for Chemical Biologyand the Department of Molecular BiologyThe Scripps Research Institute10550 North Torrey Pines Road, La Jolla, California 92037Laboratory for Bioorganic ChemistryThe Sloan-Kettering Institute for Cancer Research1275 York AVenue, New York, New York 10021ReceiVed March 25, 1997We report an antibody that is remarkable in that it catalyzesboth steps of an important synthetic transformation, the Rob-inson annulation. The Robinson annulation which accomplishes,in net terms, the conversion of a f c occupies a key role inorganic synthesis.
124 citations
01 Jan 1991
TL;DR: The development of cyclization reactions that are mild and general has been a recurring theme since the emergence of organic synthesis as a discipline as discussed by the authors, and these reactions have all the advantages of their bimolecular counterparts, such as predictability and functional group tolerance.
Abstract: Reactions that form rings are the central steps in the synthesis of cyclic organic compounds, and the development of cyclization reactions that are mild and general has been a recurring theme since the emergence of organic synthesis as a discipline. Although they have been recognized only recently, intramolecular addition reactions of radicals (hereafter called cyclizations) are among the most powerful tools at the disposal of the synthetic chemist. These radical cyclization reactions have all the advantages of their bimolecular counterparts, such as predictability and functional group tolerance; furthermore, because of the entropic advantages, cyclization reactions are of much broader scope.
46 citations
TL;DR: In this article, the preparation of α-RSe substituted carbonyl compounds and nitriles and their conversion to olefins by thermolysis of the derived selenoxides were discussed.
Abstract: Hydrogenation and dehydrogenation reactions play a key role in synthetic organic chemistry. The discoveries that selenium and sulfur substituents could be easily introduced α to a variety of acidifying functional groups, and that these derivatives could be smoothly converted to olefins by selenoxide or sulfoxide syn elimination under mild conditions greatly broadened the range of α,β-unsaturated carbonyl compounds that could be prepared from their saturated analogs. This chapter covers the preparation from enols or enolates of α-RSe substituted carbonyl compounds and nitriles and their conversion to olefins by thermolysis of the derived selenoxides. Other procedures for preparing these compounds are discussed in a limited way, and they are included in the tables, but the two-step dehydrogenation is by far the most frequently used.
The rapid acceptance of the selenoxide elimination as a synthetic procedure was the result of two factors: the ease with which many organoselenium compounds could be prepared using readily available, powerful electrophilic and nucleophilic selenium reagents, and the mild conditions (−50° to 40°) under which selenoxides fragment to olefins. Recognized selenoxide eliminations to form olefins were reported in 1967 and 1970, well after the related sulfoxide eliminations had been studied extensively. The application of the sulfoxide and selenoxide eliminations were reported almost simultaneously by several groups in 1973. These reactions have been the subject of several reviews. The principal procedures and reagents for the preparation of the requisite selenium compounds were also identified at that point.
Preparations discussed in this chapter are
Method A: Reaction of enolates, enols, enol ethers, and enamines with benzeneselenenyl chloride or bromide, or diphenyl diselenide.
Method B: Reaction of enols with seleninylating agents [C6H5Se(O)Cl, (C6H5SeO)2O].
Method C: Nucleophilic substitution of α-halo carbonyl compounds with metal selenolates.
Method D: Alkylation of α-phenylseleno carbonyl compounds and acylation of α-lithio selenides or selenoxides.
Keywords:
alpha, beta-unsaturated carbonyl compounds;
syn-elimination;
stereochemistry;
selenoxide;
seleno groups;
selenides;
mechanisms;
alpha, beta-unsaturated aldehydes;
alpha, beta-unsaturated ketones;
alpha, beta-unsaturated carboxylic acid derivatives;
alpha, beta-unsaturated lactones;
alpha-seleninylated carbonyls;
beta-carbonyls;
alpha, beta-unsaturated nitriles;
method comparisons;
oxidation;
Saegusa oxidation;
electrophilic reagents;
alpha, beta-unsaturated lactams;
alpha, beta-unsaturated amides;
alpha, beta-unsaturated imides;
alpha, beta-unsaturated beta-dicarbonyl compounds;
dehydroamino acids;
scope;
limitations;
experimental procedures
22 citations
TL;DR: Under zinc chloride catalysis, a number of 2-cyanoalk-2-enones representing various ring sizes were found to undergo facile cycloaddition with several selected conjugated dienes as discussed by the authors.
20 citations
TL;DR: A flexible synthetic strategy is developed and provides access to highly substituted tricycles related to quassinoids and triterpenes as well as reactivity of two new bicyclic cyclohexenones with several Nazarov reagents.
19 citations