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The use of dimethyl sulfoxide as an oxidizing agent began with the discoveries by Kornblum and co‐workers that certain α‐bromo ketones were converted into glyoxals under mild conditions by treatment with dimethyl sulfoxide, and that primary tosylates such as n ‐octyl tosylate were converted into the corresponding aldehydes using dimethyl sulfoxide and sodium bicarbonate at 150° for 3 minutes. The initial step of the reactions involves a displacement by dimethyl sulfoxide giving an alkoxysulfonium ion and this species undergoes a 1,2 elimination assisted by base to give the carbonyl product A few years later it was discovered that alcohols were oxidized at room temperature to carbonyl compounds by dimethyl sulfoxide, dicyclohexylcarbodiimide (DCC), and phosphoric acid. This reaction was immediately recognized as an effective and mild procedure for sensitive substrates, and the extensive studies by this group and the development of alternative variations elsewhere have been the subject of several earlier reviews. The course of the Moffatt procedure is summarized. The key intermediate in this process is the oxysulfonium ylide, which appears to be common to all of the variations of dimethyl sulfoxide oxidations, and which reacts intramolecularly to give the products. Other related procedures that were soon developed utilize dimethyl sulfoxide activated by acetic anhydride, phosphorus pentoxide, sulfur trioxide/pyridine complex, and chlorine. Reaction of alcohols with phosgene to give chloroformates which react with dimethyl sulfoxide to give alkoxysulfonium ions, followed by reaction with triethylamine, also effects oxidation. The reaction of the complexes of dimethyl sulfide and chlorine or N ‐chlorosuccinimide (NCS) with alcohols is proposed to give the same alkoxysulfonium complexes, which are efficiently converted into carbonyl products upon addition of triethylamine. Electrochemical activation of sulfides has also been successfully utilized. The activation of dimethyl sulfoxide is effected by many reagents, and these reactions as well as those involving activated sulfides evidently involve the alkoxysulfonium ion and the decisive oxidation step which occurs via the alkoxysulfonium ylide in all the reactions. Activation of dimethyl sulfoxide by oxalyl chloride, has become the most used of these oxidation procedures, but several of the other methods are also convenient and efficient.
The use of dimethyl sulfoxide as an oxidizing agent began with the discoveries by Kornblum and co‐workers that certain α‐bromo ketones were converted into glyoxals under mild conditions by treatment with dimethyl sulfoxide, and that primary tosylates such as n ‐octyl tosylate were converted into the corresponding aldehydes using dimethyl sulfoxide and sodium bicarbonate at 150° for 3 minutes. The initial step of the reactions involves a displacement by dimethyl sulfoxide giving an alkoxysulfonium ion and this species undergoes a 1,2 elimination assisted by base to give the carbonyl product A few years later it was discovered that alcohols were oxidized at room temperature to carbonyl compounds by dimethyl sulfoxide, dicyclohexylcarbodiimide (DCC), and phosphoric acid. This reaction was immediately recognized as an effective and mild procedure for sensitive substrates, and the extensive studies by this group and the development of alternative variations elsewhere have been the subject of several earlier reviews. The course of the Moffatt procedure is summarized. The key intermediate in this process is the oxysulfonium ylide, which appears to be common to all of the variations of dimethyl sulfoxide oxidations, and which reacts intramolecularly to give the products. Other related procedures that were soon developed utilize dimethyl sulfoxide activated by acetic anhydride, phosphorus pentoxide, sulfur trioxide/pyridine complex, and chlorine. Reaction of alcohols with phosgene to give chloroformates which react with dimethyl sulfoxide to give alkoxysulfonium ions, followed by reaction with triethylamine, also effects oxidation. The reaction of the complexes of dimethyl sulfide and chlorine or N ‐chlorosuccinimide (NCS) with alcohols is proposed to give the same alkoxysulfonium complexes, which are efficiently converted into carbonyl products upon addition of triethylamine. Electrochemical activation of sulfides has also been successfully utilized. The activation of dimethyl sulfoxide is effected by many reagents, and these reactions as well as those involving activated sulfides evidently involve the alkoxysulfonium ion and the decisive oxidation step which occurs via the alkoxysulfonium ylide in all the reactions. Activation of dimethyl sulfoxide by oxalyl chloride, has become the most used of these oxidation procedures, but several of the other methods are also convenient and efficient.
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.
Das durch eine SnCl4‐katalysierte Diels‐Alder‐Reaktion dargestellte Norboman (II) geht unter der Einwirkung von Na/NH3 in das Diol 6 (III), bei der Hydrierung an Pd/C in das Ketol (IV) über; (Aus (IV) erhält man durch Jones‐Oxidation (oder durch Oxidation mit DMSO/Trifluoracetanhydrid; Ausb. über 90%) und Methylierung des entstehenden Isomerengemisches (V) (endo:exo 9:1) das Diketon (VI), das sowohl mit Methylentriphenylphosphoran als auch mit Triethylorthoformiat/HCI regioselektiv an der Seitenkette, mit Methyl‐Li dagegen unter Beteiligung beider Carbonylgruppen und Bildung von (IX) reagiert.
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