Corey procedure

Corey procedure 243 Corey lactone 68 ff., 72 f. Corey-Nicolaou... 

Corey and Reichard described a more efficient synthesis of the fluoxetine enantiomers.15 This synthesis features a catalytic reduction of prochiral ketone 12 to install the correct absolute stereochemistry at C-3. In this respect this method is very similar to the one previously described by Robertson et al.10 However, the major advantage of the Corey procedure is that the reduction utilizes chiral enzyme-like catalysts to induce the correct stereochemistry and both enantiomers of the catalyst are available (15 and 16). 

The oxidation reaction can be extended to heterocyclic alcohols (eq 27) and the Corey procedure gives the expected esters (eq 28).2> ... 

D. M. Perrine and J. Kagan, A side reaction in the S5mthesis of 2-eth5mylthiophene from 2-thiophene-carboxaldehyde by the Corey procedure and an inproved synthesis of 2,2 5, 2 -terthiophene, Heterocycles, 24, 365-368 (1986). 

The bis-branched-chain 3-pentulose (9) was formed in the formose reaction using thiamine HQ as catalyst under controlled conditions. The spiro-eponde (10), synthesized from levoglucosenone by the Corey procedure (NaH/McjSI/DMSO-THF), was used to prepare the branched derivatives (11) - (14). ... 

In the case of [l-j8- H]cyclosporin A (11) (Figure 10.4) the keto precursor 12, which is readily accessible through oxidation of 11 with NCS-dimethyl sulfide (Kim-Corey procedure) or DMSO, DCCI, and dichloroacetic acid (Pfitzer-Moffat variant), exists as a keto-enol mixture, eliminating one of the adjacent stereogenic centers. Accordingly, the subsequent NaB H4 reduction generated a set of four diastereomers [ H]U and 13-15. The required diastereomer, however, was formed in 95% stereoselectivity and the residual diastereomers could be separated by two consecutive preparative HPLC operations . 

Cyclopentene derivatives with carboxylic acid side-chains can be stereoselectively hydroxy-lated by the iodolactonization procedure (E.J. Corey, 1969, 1970). To the trisubstituted cyclopentene described on p. 210 a large iodine cation is added stereoselectively to the less hindered -side of the 9,10 double bond. Lactone formation occurs on the intermediate iod-onium ion specifically at C-9ot. Later the iodine is reductively removed with tri-n-butyltin hydride. The cyclopentane ring now bears all oxygen and carbon substituents in the right stereochemistry, and the carbon chains can be built starting from the C-8 and C-12 substit""" ... 

Because the Corey synthesis has been extensively used in prostaglandin research, improvements on the various steps in the procedure have been made. These variations include improved procedures for the preparation of norbomenone (24), alternative methods for the resolution of acid (26), stereoselective preparations of (26), improved procedures for the deiodination of iodolactone (27), alternative methods for the synthesis of Corey aldehyde (29) or its equivalent, and improved procedures for the stereoselective reduction of enone (30) (108—168). For example, a catalytic enantioselective Diels-Alder reaction has been used in a highly efficient synthesis of key intermediate (24) in 92% ee (169). 

Pyridinium p-toluenesulfonate, r-BuOH or 2-butanone, heat, 80-99% yield. This method also cleaves the MOM ether and has the advantage that it cleanly cleaves allylic ethers that could not be cleaved by Corey s original procedure. 

This method for the preparation of cyclobutanone via oxaspiropentane is an adaptation of that described by Salaiin and Conia. The previously known large-scale preparations of cyclobutanone consist of the reaction of the hazardous diazomethane with ketene, the oxidative degradation or the ozonization in presence of pjrridine of methylenecyclobutane prepared from pentaerythritol, or the recently reported dithiane method of Corey and Seebach, which has the disadvantage of producing an aqueous solution of the highly water-soluble cyclobutanone. A procedure involving the solvolytic cyclization of 3-butyn-l-yl trifluoro-methanesulfonate is described in Org. Syn., 54, 84 (1974). 

Corey states that their experience shows the above procedure for conversion of (26) (29) is the method of choice for ring expansion of a, -unsaturated... 

Scheme 6. Corey s synthesis of gibberellic acid GA3 (22) employing the Upjohn catalytic dihydroxylation procedure.

Closely related to the polyepoxide cascade procedure for the synthesis of polycyclic systems is Corey s biomimetic-type, nonenzymatic, oxirane-initiated (Lewis acid-promoted) cation-olefin polyannulation. By this strategy, compound 96, containing the tetracyclic core of scalarenedial, was constructed by exposure of the acyclic epoxy triene precursor 95 to MeAlCl2-promoted cyclization reaction conditions (Scheme 8.25) [45]. 

It is appropriate to conclude this section with a brief mention of the procedure published over 20 years ago by Corey and Chaykovsky45, with which /1-ketosulphoxidcs are desulphinylated with Al/Hg in wet THF to give ketones. Such reactions are very important synthetically and formally constitute a reduction at both sulphur and carbon. For their... 

The catalyst played an important role in the asymmetric synthesis of Corey lactone based on high diastereofacial selective Diels-Alder reaction between chiral acrylate 37 and 5-benzyloxymethylcyclopentadiene [41] (Equation 3.9). The cycloadduct 38 was then converted into chiral Corey lactone [42] by a three-step procedure. 

Pioneering work on the desulphonylation of jS-ketosulphones was carried out by Corey and Chaykovsky - . This reaction was part of a sequence which could be used in the synthesis of ketones, as shown in equation (53). The main thrust of this work was in the use of sulphoxides, but Corey did stress the merits of both sulphones and sulphonamides for different applications of this type of reaction. The method soon found application by Stetter and Hesse for the synthesis of 3-methyl-2,4-dioxa-adamantane , and by House and Larson in an ingenious synthesis of intermediates directed towards the gibberellin skeleton, and also for more standard applications . Other applications of the method have also been madealthough it does suffer from certain limitations in that further alkylation of an a-alkyl- -ketosulphone is a very sluggish, inefficient process. Kurth and O Brien have proposed an alternative, one-pot sequence of reactions (equation 54), carried out at — 78 to — 50°, with yields better than 50%. The major difference between the two routes is that the one-pot process uses the desulphonylation step to generate the enolate anion, whereas in the Corey-House procedure, the desulphonylation with aluminium amalgam is a separate, non-productive step. 

Iodotrimethylsilane formed in situ from the reaction of chlorotrimethylsilane and sodium iodide, also effects the conversion of 2-ene-l,4-diols to 1,3-dienes (equation 16)46. Allylic thionocarbonates on heating with triphenylphosphite undergo deoxygenation (Corey-Winter reaction) to generate olefins47. This procedure has been used for making hexatrienes (equation 17)47b. 

Chiral Hydrazone Systems. In 1976, Corey and Enders34 demonstrated the great synthetic potential of metalated dimethylhydrazones as highly reactive intermediates in regio- and diastereoselective C C bond formation reactions. The procedure for carrying out the electrophilic substitution reaction... 

Addition of triethylamine to the oxazaborolidine reaction system can significantly increase the enantioselectivity, especially in dialkyl ketone reductions.79 In 1987, Corey et al.80 reported that the diphenyl derivatives of 79a afford excellent enantioselectivity (>95%) in the asymmetric catalytic reduction of various ketones. This oxazaborolidine-type catalyst was named the CBS system based on the authors names (Corey, Bakshi, and Shibata). Soon after, Corey s group81 reported that another fi-methyl oxazaborolidine 79b (Fig. 6-6) was easier to prepare and to handle. The enantioselectivity of the 79b-catalyzed reaction is comparable with that of the reaction mediated by 79a (Scheme 6-36).81 The -naphthyl derivative 82 also affords high enantioselectivity.78 As a general procedure, oxazaborolidine catalysts may be used in 5-10 mol%... 

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