Iodide, carbonyl bromine

As inert as the C-25 lactone carbonyl has been during the course of this synthesis, it can serve the role of electrophile in a reaction with a nucleophile. For example, addition of benzyloxymethyl-lithium29 to a cold (-78 °C) solution of 41 in THF, followed by treatment of the intermediate hemiketal with methyl orthoformate under acidic conditions, provides intermediate 42 in 80% overall yield. Reduction of the carbon-bromine bond in 42 with concomitant -elimination of the C-9 ether oxygen is achieved with Zn-Cu couple and sodium iodide at 60 °C in DMF. Under these reaction conditions, it is conceivable that the bromine substituent in 42 is replaced by iodine, after which event reductive elimination occurs. Silylation of the newly formed tertiary hydroxyl group at C-12 with triethylsilyl perchlorate, followed by oxidative cleavage of the olefin with ozone, results in the formation of key intermediate 3 in 85 % yield from 42. 

Carboxylic acids, a-bromination of 55, 31 CARBOXYLIC ACID CHLORIDES, ketones from, 55, 122 CARBYLAMINE REACTION, 55, 96 Ceric ammonium nitrate [Ammonium hexa mtrocerate(IV)[, 55, 43 Chlorine, 55, 33, 35, 63 CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Cinnamomtnle, a-phenyl- [2-Propeneni-tnle 2,3-diphenyl-], 55, 92 Copper(l) iodide, 55, 105, 123, 124 Copper thiophenoxide [Benzenethiol, copper(I) salt], 55, 123 CYCLIZATION, free radical, 55, 57 CYCLOBUTADIENE, 55, 43 Cyclobutadieneiron tricarbonyl [Iron, tn-carbonyl(r)4-l,3-cyclo-butadiene)-], 55,43... 

Iodocarbonyls are excellent substrates for atom transfer cyclization, as shown by examples from our recent work in Scheme 29.19-129 When two carbonyl (or cyano) groups are present, bromides can also serve as radical precursors. Photolysis with 10% ditin usually provides excellent yields of kinetic products at high concentration, and alkene substituents often dictate the regioselectivity. The y-iodo ester products are particularly versatile for subsequent transformations, which can often be conducted in situ. Although tertiary iodine products sometimes go on to give lactones or alkenes, primary and secondary iodides can often be isolated if desired. The last example is particularly noteworthy the kinetic product from the cyclization presented in Scheme 27 is trapped, because bromine atom transfer is much more rapid that reverse cyclization. 

Complexes containing from one to six carbonyl groups are known and all obey the 18-electron rule. The colorless salt [Tc(CO)6]A1C14 is formed by the reaction of [Tc(CO)5C1] with A1C13 under 300 atm CO pressure and is soluble in THF, acetone, and methanol and stable in aqueous solution (65). The carbonyl halides [Tc(CO)5X] (X = Cl, Br, I) may be prepared by the reaction of the halogen with [Tc2(CO)10]. Reaction with chlorine and bromine occurs readily at room temperature but reaction with iodine is extremely slow. The iodide has been prepared by the high-pressure carbonylation of [Tc(CO)4I]2 (45). An alternative... 

Hexacarbonylchromium(O) is readily attacked by chlorine giving CrCb, CO, and COCI2. Bromine and iodine do not attack Cr(CO)6 to any substantial extent at room temperature. The chromium tricarbonyl arene complexes, Cr(CO)3( -arene), are readily oxidized at room temperature by I2 to give Cris this is a conveitient preparative method for the anhydrous iodide. Although the oxidation of the tricarbonyl arene derivatives of chrontium with I2 does not show evidence of intermediate carbonyl complexes in oxidation states >0, the corresponding molybdenum(O) compounds give a series of carbonyl iodides of molybdenum(II), for example, the ionic [Mo(CO)3 ( ) -arene)]I. 

Many classical reactions have been recognized to proceed according to this halogen-ATC catalysis mechanism examples are the dehydroiodination of secondary iodides by Pt° [10], the bromination of [Mn2(CO)io], and the exchange of carbonyls by phosphines or isonitriles [50]. 

Oxidation and Bromination of Other Functional Groups. Selective oxidation of alcohols may be achieved using a 1 1 complex of NBS and tetrabutylammonium iodide, whereas 1,2-diols are converted into 1,2-diketones using iV-bromosuccini-mide. An efficient and mild procedure has been reported for the preparation of benzoic acids via oxidation of aromatic carbonyl compounds by employing NBS and mercuric acetate. Selective and efficient oxidation of sulfides to sulfoxides has been achieved with NBS in the presence of /3-cyclodextrin in water. Epoxides and aziridines are conveniently oxidized to the corresponding a-hydroxy or Q -amino ketones using cerium(IV) ammonium nitrate and NBS. ... 

A method for removal of halogen from a-bromoketones (19) utilizes a combination of Lil and BF3 as the reagents. The hard-hard interaction between the carbonyl oxygen and the boron atom serves to activate the a-bromine toward attack by the soft iodide ion. The reaction is in accord with Saville s rule. 

The copolymer 174 was prepared from diaUcyl thienylated benzodithiophene (173) and perfluororalkyl-carbonyl substituted thieno[3,4-h]thiophene (172) monomers (Scheme 41). Thus, reaction of thieno[3,4-6]thiophene-2-carbaldehyde (150) with heptadecafluorooctyl iodide in the presence of methyllithium to form 170 was followed by oxidation with Mn02 giving ketone 171. Bromination with two equivalents of NBS furnished dibromide 172, and this was Stille cross-coupled with 173 in the presence of Pd2(dba)3 to obtain the copolymer 174 [63]. 

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