Formation of 14.alpha.-cardenolides from 21-acetoxy-20-keto steroids

Lenz, George R.; Schulz, John A.

doi:10.1021/jo00406a006

Cited by 10 publications

References 8 publications

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Reductions by Metal Alkoxyaluminum Hydrides. PartII. Carboxylic Acids and Derivatives, Nitrogen Compounds, and Sulfur Compounds

Málek

1988

Organic Reactions

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In continuation of the previous review on reductions by metal alkoxyaluminum hydrides, this chapter is devoted to reductions of carboxylic acids and their derivatives, open‐chain and heterocyclic nitrogen compounds, and open‐chain and heterocyclic sulfur compounds by alkoxyaluminum hydrides, metal alkoxyaluminum hydrides, and chiral metal alkoxyaluminohydride complexes. Emphasis is placed on the scope, limitations, and the synthetic utility of metal alkoxyaluminum hydrides. Accepted views on reaction mechanisms are mentioned briefly. Discussion of alternative methods of reduction, particularly those using other metal hydrides or complex metal hydrides, is limited to examples of the most important transformations of functional groups; reducing properties of these hydrides and hydride reagents such as borane–dimethyl sulfide, amine boranes, haloboranes, organoboranes, sodium borohydride–pyridine, sodium borohydride–triphenyl borate, sodium borohydride—transition‐metal complexes, potassium triisopropoxyborohydride, and sodium triacyloxyborohydrides have been reported in several papers and reviews. Monographs and reviews summarize reductions with metal alkoxyaluminum hydrides and asymmetric reductions with chiral lithium alkoxyaluminum hydrides and chiral boron reagents.

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Reductions by Metal Alkoxyaluminum Hydrides. PartII. Carboxylic Acids and Derivatives, Nitrogen Compounds, and Sulfur Compounds

Málek

1988

Organic Reactions

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Simmons‐Smith Cyclopropanation Reaction

2001

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Almost 30 years after Emschwiller prepared IZnCH 2 I, Simmons and Smith discovered that the reagent formed by mixing a zinc‐copper couple with CH 2 I 2 in ether could be used for the stereospecific conversion of alkenes to cyclopropanes. Nowadays, the Simmons‐Smith cyclopropanation reaction is one of the most widely used reactions in the organic chemist's arsenal for the conversion of olefins into cyclopropanes. This popularity is mainly due to the stereospecificity of the reaction with respect to the double bond geometry and its compatibility with a wide range of functional groups. The chemoselectivity of the reaction toward some olefins is excellent and very few side reactions are observed with functionalized substrates. The metal carbenoid is electrophilic in nature and electron‐rich alkenes usually react much faster than electron‐poor alkenes. Furthermore, the ability to use proximal hydroxy or ether groups to dictate the stereochemical outcome of the CC bond forming process was recognized early on, and this unique property has been successfully exploited on numerous occasions. It has been recognized that halomethylmetal reagents are powerful synthetic tools for the stereoselective addition of a methylene unit to chiral acyclic allylic alcohols and allylic ethers. In addition, the use of halomethylzinc reagents in the presence of chiral additives is one of the few ways to cyclopropanate allylic alcohols efficiently and with good enantiocontrol. Carbenoids can be divided into the following two classes: (1) those of general structure MCH 2 X and (2) those corresponding to M = CH 2 . This chapter is focussed exclusively on the first class in which M = Zn, Sm, or Al. Although other metal carbenoids of type MCH 2 X, such as those derived from Cu, Cd, Hg, and In, have been reported to be effective reagents for the cyclopropanation of some olefins, they have been used only sporadically, and this review does not highlight these reactions. This chapter covers cyclopropanation reactions involving haloalkylzinc, aluminum, and samarium reagents published since the comprehensive chapter in Organic Reactions by Simmons that surveyed the literature up to 1973.

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Fernandes¹

2018

Protecting‐Group‐Free Organic Synthesis

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Formation of 14.alpha.-cardenolides from 21-acetoxy-20-keto steroids

Cited by 10 publications

References 8 publications

Reductions by Metal Alkoxyaluminum Hydrides. PartII. Carboxylic Acids and Derivatives, Nitrogen Compounds, and Sulfur Compounds

Reductions by Metal Alkoxyaluminum Hydrides. PartII. Carboxylic Acids and Derivatives, Nitrogen Compounds, and Sulfur Compounds

Simmons‐Smith Cyclopropanation Reaction

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