Lactonization Corey procedure

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

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""" ... 

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. 

An effective new method for the synthesis of macrocyclic lactones has been developed by Corey and Nicolau (75). In this method both the hydroxyl and the carboxyl groups have been activated by formation of a 2-pyridin-ethiol ester. Vertaline was obtained in 67% yield when this procedure was applied to the corresponding hydroxyacid (76). 

Corey s double activation procedure (Method 2) does not use an external reagent to activate the functional group, but effects cyclization by heating a solution of the 2-pyridinethiol ester of a hydroxy acid for a prolonged period. Several pieces of evidence point to the intermediacy of 2 in this lactonization.10 If one accepts this intermediate, it follows that a hydroxy(2-pyridinethiolJ ester, heavily substituted near the reaction centers (i.e., near the hydroxyl and acyl groups), would encounter a high... 

Method 2. Corey s double activation method for lactone formation is patterned after Mukaiyama s procedure for peptide formation and involves refluxing a solution of the 2-pyridinethiol ester of a hydroxy acid in a high-boiling solvent for a prolonged period of time.6... 

Table 5 shows the yields of the lactones 56 obtained by an intramolecular cycli-zation of the -halogeno carboxylic acids 55 using ceaum ions. The yields are compared to those obtein l by Corey and Nicolaou [2] using the pyridinethiol procedure. 

The t synthesis of erydironolide B, the biosynthetic progenimr of all the erythromycins, employed a Baeyer-Villiger oxidation of die substituted cyclohexanone (31 equation 18). The oxidation was surprisingly slow using customary procedures, but Corey et alP found diat forcing conditions provided the required lactone (32). 

In other reports, /i-cyclodextrins have been used to induce asymmetry in borohydride reduction of ketones, a diastereoselective reduction has been controlled by a n-allyltricarbonyliron lactone tether , a phosphinamide has been combined with a dioxaborolidine unit as an activated, directed catalyst for ketone reduction, reductive amination using benzylamine-cyanoborohydride converts 3-hydroxy ketones into syn-1,3-amino alcohols, l-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propan-1 -one has been reduced diastereoselectively, and production of chiral alcohols via (i) Itsuno-Corey and Brown procedures and (ii) lithium aluminium hydride modified by chiral nucleophiles has been reviewed. 

The first totai synthesis of the ichthyotoxic marine naturai product (-)-apiyoiide A was accomplished by Y. Stenstrom and co-workers. The compound has a 16-membered lactone ring, four (Z)-double bonds, as well as a stereogenic center. Numerous macroiactonization protocols were tested, but most of them gave the diolide (dimer) except for the Corey-Nicoiaou procedure. 

Esters and lactones. Swiss chemists have used a procedure similar to that of Corey and Nicolaou (5, 260) for preparation of esters and lactones, but they carry out the reaction in the presence of 1 eq. of AgBp4 or AgC104. Coordination of an S-2-pyridylthiocarboxylate with silver ion permits rapid esterification at 20° in a few minutes. If the silver salt is omitted in the example cited, the yield of ester is only 5% after 7 days at 20°. 

Claisen rearrangement of 3,4-unsaturated glycosides to C4-branched derivatives provided useful intermediates for the total synthesis of thromboxanes (Scheme 20). First reported independently by Corey et al. [41] and Hernandez [42],both the Eschenmoser amide acetal and the Johnson orthoester procedure afforded good results for the conversion of allylic alcohol 99 (R = Me, R = H) to the respective amide or ester 100. Corey et al. further transformed the former compound to lactone 101, previously described as a precursor for the total synthesis of thromboxane B2 (102). A number of further derivatives 100 (R = allyl, R = H or TBDMS, R = NMe2 or OEt) and its C2-epimer were prepared in a similar manner during later thromboxane synthetic studies [43,44]. 

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