Sterische Effekte bei
 endo, exo
 ‐Tetracyclo[6.2.1.1
 3,6.
 0
 2,7
 ]‐dodecanen: Einfluß von 4‐Substituenten auf die Solvolyse der 11‐epimeren Sulfonate
 1)

Lenoir, Dieter; Frank, Robert M.

doi:10.1002/cber.19811141014

Cited by 16 publications

(1 citation statement)

References 23 publications

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“…A variety of stereoselectivities of acyclic and acyclic chiral compounds were studied; the force field gave excellent agreement with experiment and provided strong support to the Felkin model. The force field was used to make the nonintuitive conclusion that equatorial rather than axial attack would occur on benzocycloheptanones (13) in spite of the obvious similarity to cyclohexanones (14) . This was verified experimentally for LAH reductions.…”

Section: E Cope and Claisen Rearrangementsmentioning

confidence: 99%

Transition-state modeling with empirical force fields

Eksterowicz¹,

Houk²

1993

Chem. Rev.

166

109

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Section: E Cope and Claisen Rearrangementsmentioning

confidence: 99%

Transition-state modeling with empirical force fields

Eksterowicz¹,

Houk²

1993

Chem. Rev.

166

109

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Lithioalkenes from Arenesulfonylhydrazones

Chamberlin¹,

Bloom²

1990

Organic Reactions

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Among the most important of all carbon–carbon bond forming methods are reactions of electrophiles with organolithium compounds. As part of this large group of reagents, regio‐ and stereoselectively prepared alkenyllithiums are valuable intermediates for the controlled construction of a wide variety of substituted alkenes. This chapter covers a highly selective procedure for the preparation of relatively complex alkenyllithium species from ketone arenesulfonylhydrazones. The reaction of these vinyl anions with various electrophiles affords a wide range of specifically substituted di‐, tri‐, and tetrasubstituted alkenes. This methodology arose from early studies on the thermal decomposition of sodium salts of p ‐toluenesulfonylhydrazones (tosylhydrazones) and two subsequent modifications of that reaction. In the early 1950s Bamford and Stevens reported a new reaction based on the thermally induced decomposition of ketone tosylhydrazone monosodium salts, producing products derived either from carbene intermediates (aprotic conditions) or carbocations (protic conditions). The protic reaction is of marginal synthetic value because mixtures of carbocation‐derived products are normally obtained; however, the aprotic reaction has found widespread use in the synthesis of multicyclic, strained hydrocarbons. Both reactions have been covered in reviews. It was later found that treating a tosylhydrazone with ethereal alkyllithium, instead of the much weaker alkoxide bases used previously, results in a very different reaction. Under these conditions an alkene derived from an alkenyllithium intermediate is the sole product. This process, commonly known as the Shapiro reaction, has been applied to the preparation of a large number of structurally diverse alkenes and is the subject of an earlier review. Unfortunately, trapping of the vinyllithium intermediate proved to be so inefficient and unpredictable under a number of different conditions that the reaction was of little utility as a method of vinyllithium generation. In 1975, however, conditions were reported that not only gave high yields of olefin but also nearly quantitative incorporation of electrophiles. The only remaining drawback was that efficient trapping of tosylhydrazone‐derived vinyllithiums occurs only with the use of excess base (≥3 equivalents of n ‐butyllithium) rather than the stoichiometric 2 equivalents required by the mechanism, even though the olefin yield was quite good. Eventually, this nagging stoichiometry problem, which necessitates the use of excess electrophile as well as excess base, was solved by the use of ketone 2,4,6‐triisopropylbenzenesulfonylhydrazones (trisylhydrazones) in place of tosylhydrazones. An account of some synthetically useful aspects of the Shapiro reaction and its subsequent variants has appeared. This review covers the generation of vinyllithiums from arenesulfonylhydrazones under conditions that allow efficient trapping with electrophiles other than proton sources. Examples in which trapping of the intermediate vinyllithium was not demonstrated, including reactions conducted under standard “Shapiro reaction” conditions, are excluded.

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The Oxidation of Alcohols by Modified Oxochromium( VI )–Amine Reagents

Luzzio

1998

Organic Reactions

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The development of oxochromium(VI)‐amine reagents as oxidants in organic synthesis has evolved since the early studies of Sisler which described the use of adducts of heterocyclic nitrogen bases and chromium(VI) oxide. The later work of Sarrett and coworkers in steroid synthesis soon established the utility of chromium(VI) oxide‐pyridine adducts as the first selective oxochromium(VI)‐amine reagents. Several modifications of the Sarrett oxidation followed. The present concern with the toxicity and environmental implications of oxochromium(VI) has provided encouragement for the study and use of catalytic oxochromium reagents in conjunction with stoichiometric co‐oxidants such as peroxides. Such technology is welcome, particularly when applied to the large‐scale preparations found in industry where the disposal of byproducts is a constant problem. Modified oxochromium(VI)‐amine reagents on polymer supports have been prepared and examined with the objective of providing a regenerable reagent system which is serviceable on a practical scale. A significant improvement in routine oxidations utilizing PCC and PDC entails the addition of adsorbents such as Celite®, alumina, silica gel, molecular sieves, or zeolites. The distinct advantages associated with the use of adsorbents in oxochromium(VI)‐amine‐mediated oxidations are discussed. The importance of buffers and desiccants in oxochromium(VI) oxidations is discussed. Virtually any number of oxochromium(VI)‐amine reagents may be prepared by varying the amine ligand and/or acid species associated with oxochromium(VI), and many of these compounds have been tested using simple substrate alcohols for oxidation to carbonyl compounds. The search for a milder and more efficient oxidant than the Sarrett‐type oxochromium(VI) reagent systems as well as the nonchromium oxidants based on dimethyl sulfoxide or dimethyl sulfide led to an examination of the utility of pyridinium chlorochromate (PCC) in selective oxidations of alcohols. PCC was superior in terms of ease of preparation, shelf stability and economy. Since the introduction of PCC in 1975 the reagent has become a commercially available “textbook” compound and is usually the reagent of choice for routine large and small scale oxidations of alcohols to carbonyl compounds. Unlike the oxochromium(VI)‐pyridine adducts, PCC is an acid salt, and its properties have proven advantageous in a number of tandem oxidative reactions such as oxidative transpositions and oxidative cationic cyclizations. Several reviews address the versatility of PCC and its extension to many different types of oxidative conversions in single and multistep organic syntheses. While PCC was gaining widespread use, the utility of pyridinium dichromate (PDC) in solvents such as dimethylformamide (DMF) and dichloromethane was reported. PDC/DMF was useful for oxidizing allylic alcohols to the corresponding, α,β‐unsaturated carbonyl compounds and non‐conjugated aldehydes and primary alcohols to the corresponding carboxylic acids. The utilization of beyond the simple oxidation of alcohols, and it is now employed for various transformations. Many other types of substituted pyridines, nitrogen heterocycles and amines form chromates, dichromates, and chlorochromates which allow many different types of oxidative processes for a wide range of substrate molecules. This chapter surveys the many applications of oxochromium(VI) complexes in oxidative conversions of alcohols to carbonyl compounds. Alternative reagent systems based on modifications involving ligands, buffering agents, or adsorbents, as well as nonchromium(VI) oxidants are discussed. A variety of substrates have been included in the Tables so as to guide the synthetic chemist in selecting reagents and conditions that will be optimal for a given transformation. Oxidative conversions of alcohols through transpositions and cationic cyclizations giving carbonyl compounds as endproducts are included.

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Sterische Effekte bei endo, exo ‐Tetracyclo[6.2.1.1 ^3,6. 0 ^2,7 ]‐dodecanen: Einfluß von 4‐Substituenten auf die Solvolyse der 11‐epimeren Sulfonate ¹⁾

Cited by 16 publications

References 23 publications

Transition-state modeling with empirical force fields

Transition-state modeling with empirical force fields

Lithioalkenes from Arenesulfonylhydrazones

The Oxidation of Alcohols by Modified Oxochromium( VI )–Amine Reagents

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Sterische Effekte bei endo, exo ‐Tetracyclo[6.2.1.1 3,6. 0 2,7 ]‐dodecanen: Einfluß von 4‐Substituenten auf die Solvolyse der 11‐epimeren Sulfonate 1)

Cited by 16 publications

References 23 publications

Transition-state modeling with empirical force fields

Transition-state modeling with empirical force fields

Lithioalkenes from Arenesulfonylhydrazones

The Oxidation of Alcohols by Modified Oxochromium( VI )–Amine Reagents

Contact Info

Product

Resources

About

Sterische Effekte bei endo, exo ‐Tetracyclo[6.2.1.1 ^3,6. 0 ^2,7 ]‐dodecanen: Einfluß von 4‐Substituenten auf die Solvolyse der 11‐epimeren Sulfonate ¹⁾