Reagent Collins

Collins reagent can be prepared and isolated or generated in. situ. Isolation of the reagent often leads to improved yields. 

Coformycin, 2 -deoxy—see Pentostatin Colchicine synthesis, 1, 472 isothiazoles in, 6, 174 Collins reagent as oxidizing agent, 2, 170 Colour... 

The double bond transposition could also be achieved by the conversion of an intermediate for PGA2 synthesis into a 1,3-diene iron tricarbonyl complex from which PGC2 was synthesized in four steps. The Fe(CO)3 diene complex which survived the Wittig reaction was cleanly removed by Collins reagent in the subsequent step (Ref. 10). 

This is followed by hydrolysi.s of the ester moieties with potassium carbonate and reesterification of the carboxy moiety with diazomethane to produce intermediate 65. The solitary free alcoholic hydroxyl at C-9 is oxidized with Collins reagent and the silyl ether groups are removed with acetic acid to give enprostil (63) [15]. 

The chief drawbacks to using the Collins reagent are the nuisance involved in preparing pure dipyridine chromium VI) oxide,6 its hygroscopic nature5 and its propensity to enflame during preparation.2 3 5 The present method avoids these difficulties by simply preparing diehloromethane solutions of the complex directly.7 In... 

The Collins reagent in CH2CI2 oxidizes silylated primary alcohols in preference to the more hindered silylated secondary alcohols, as described for oxidation of the prostaglandin intermediate 2963 to the rather labile aldehyde 2964, which is immediately subjected to a Horner-Wittig-reaction to introduce the lower side chain [206] (Scheme 12.61). 

Scheme 5. Reaction conditions i, reductive amination ii, protection of amino group iii, Collins reagent iv, Ph3F CHCioH2i" v, hydrolysis vi, Hg(OAc>2 vii, NaBH4 viii, l-decen-3-one ix, ethanedithiol x, Raney Ni xi, HCl-EtOH.

Aldehydes are further oxidized to carboxylic acids, RCOOH. To get aldehydes, milder reagents, such as the Jones (diluted chromic acid in acetone) or Collins reagent (a complex of CrOj with 2 mol of pyridine), are used. 

Similar to the Sarrett Reagent. The major difference appears that the classical Collins Reagent is filtered while the Sarrett is used in pyridine. 

An alternative furan-based jasmone synthesis has been accomplished through oxidative cleavage of this heterocyclic ring (73AJC2671). Thus, the furan (85) was oxidized with Collins reagent to the enedione (86) and the conjugated double bond reduced with sodium dithionite. Base cyclization then gave pure (Z)-jasmone (Scheme 21). 

Treatment of 6-lithio-3,4-dihydro-2H-pyran (660) with the epoxy iodide (661) afforded the epoxydihydropyran (662). Compound (662) cyclized on exposure to basic A1203 to a single hydroxydihydropyran (663) which was oxidized with Collins reagent to the keto aldehyde (664) containing three contiguous asymmetric centers of fixed stereochemistry (Scheme 153). The metallated dihydropyrans have also found use in the construction of keto lactones (78JA7101). 

The most widely used chromium(VI)-oxo reagents for synthetic use in organic chemistry are the Collins reagent, Cr03(py)2,273 and the Corey reagent, Cr03CrpyH+,297 with the latter being superior for the oxidation of primary alcohols to aldehydes.275... 

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