Iodides preparation from alcohols

Add 4 0 g. (4 0 ml.) of pure anihne dropwise to a cold solution of ethyl magnesium bromide (or iodide) prepared from 1 Og. of magnesium, 5 0 g. (3-5 ml.) of ethyl bromide (or the equivalent quantity of ethyl iodide), and 30 ml. of pure, sodium-dried ether. When the vigorous evolution of ethane has ceased, introduce 0 02 mol of the ester in 10 ml. of anhydrous ether, and warm the mixture on a water bath for 10 minutes cool. Add dilute hydrochloric acid to dissolve the magnesium compounds and excess of aniline. Separate the ethereal layer, dry it with anhydrous magnesium sulphate and evaporate the ether. Recrystallise the residual anihde, which is obtained in almost quantitative yield, from dilute alcohol or other suitable solvent. 

The required xanthates 1 can be prepared from alcohols 5 by reaction with carbon disulfide in the presence of sodium hydroxide and subsequent alkylation of the intermediate sodium xanthate 6. Often methyl iodide is used as the alkylating agent ... 

Radical deoxygenation of alcohols is important, and the reduction of xanthates prepared from alcohols, with Bu3SnH in the presence of AIBN is called the Barton-McCombie reaction (eq. 2.13) [37-51]. The driving force for the reaction is the formation of a strong C=0 bond from the C=S bond, approximately 10 kcal/mol stronger. This reaction can be used for various types of substrates such as nucleosides and sugars. Though methyl xanthates, prepared from alcohols with carbon disulfide and methyl iodide under basic conditions are very frequently used, other thiocarbonates, as shown in eq. 2.14, can also be employed. 

Phosphonates have also been prepared from alcohols and (Ar0)2P(=0)Cl, NEts and a TiCl4 catalyst. ° The reaction of (R0)2P(=0)H and aryl iodides with a Cul catalyst leads to aryl phosphonates. " Polymer-bound phosphonate esters have been used for olefination. Dienes are produced when allylic phosphonate esters react with aldehydes. 

The union of 51 with aldehyde 49 was achieved via the phosphonium iodide 52, prepared from alcohol 51 under very peculiar conditions (PPI13,12 then PPh3 at ultrahigh pressure [54] in buffered nonpolar medium). Addition of the phosphonium salt 52 to aldehyde 49 afforded the coupling product 53 in good yield and with an excellent ZjE selectivity (24/1). This compound represents the discodermolide carbon... 

Ether can be prepared from alcohol by a method which has great historical interest, as it was through the discovery of this method that the structure of ethers and their relation to the alcohols were first made clear. When ethyl iodide is heated with sodium ethylate ether is formed —... 

Phosphonium salt 482, which can also be prepared from alcohol 437 by treatment with methyltriphenoxyphosphonium iodide followed by triphenylphosphine, has been used in a stereoselective synthesis of 6-ep/-D-purpurosamine B (494) (Scheme 69) [122]. A Wittig reaction of the ylide generated from 482 and Cbz-L-alaninal (488) affords the Z-olefin 489. lodocyclization gives the trans-cyclocaihamatQ 490 in quantitative yield. Removal of the iodo group, hydrolysis of the acetonide, and benzoylation fhmishes 491. 

High yields of sensitive carbodiimides can be obtained from thioureas under mild conditions with cyanuric diloride and triethylamine and also with quinones Carbodiimidium salts have been introduced as novel reagents and used successfully for the preparation from alcohols of iodides, including sterically hindered compounds... 

Iodides can be prepared from alcohols via treatment of cyclic phosphite ester derivatives with iodine ... 

Preparation.— The 2-alkoxydiazaphospholidines (55), mentioned earlier in this Report, have been prepared from alcohols and their facile conversion into alkyl chlorides, bromides, and iodides with inversion of configuration at carbon has been reported (Scheme 34) a one-pot procedure is suggested for the transformation of an alcohol into an alkyl iodide. Tributyldi-iodophosporane, BU3PI2,... 

Iodides can also be prepared from alcohols by a procedure which has been shown to result in clean inversion of stereochemistry in cyclic systems. The reagents used are triphenylphosphine, diethyl azodicarboxylate, and methyl iodide. Again an alkoxyphosphonium ion is the key intermediate. 

Primary, secondary, and terriary alkyl iodides may be prepared from alcohols by treatment with chlorotrimethylsilane in the presence of sodium iodide, without rearrangement, in yields ranging from 78 to 98% (Eq. 6.54) [83]. 

Three general methods are available for the preparation of iodides from alcohols —... 

A special apparatus (Fig. Ill, 40,1) renders the preparation of iodides from alcohols a very simple operation. The special features of the apparatus are —(i) a wide bored (3-4 mm.) stopcock A which considerably reduces the danger of crystallisation in the bore of the tap of the iodine from the hot alcoholic solution (ii) a reservoir B for the solid iodine and possessing a capacity sufficiently large to hold all the alkyl iodide produced (iii) a wide tube C which permits the alcohol vapour fix)m the flask D to pass rapidly into the reservoir B, thus ensuring that the iodine is dissolved by alcohol which is almost at the boiling point. An improved apparatus is shown in Fig. Ill, 40, 2, a and b here a... 

Alkyl esters of trifluoromethanesulfonic acid, commonly called triflates, have been prepared from the silver salt and an alkyl iodide, or by reaction of the anhydride with an alcohol (18,20,21). Triflates of the 1,1-dihydroperfluoroalkanols, CF2S020CH2R can be prepared by the reaction of perfluoromethanesulfonyl fluoride with the dihydroalcohol in the presence of triethylamine (22,23). Triflates are important intermediates in synthetic chemistry. They are among the best leaving groups known, so they are commonly employed in anionic displacement reactions. 

Veratramine, C27H3g02N, occurs naturally in V. viride and V. grandi-florum and is also formed by the hydrolysis of veratrosine. It has m.p. 209-210-5°, fa] — 68° (MeOH), and yields a dihydro-derivative, m.p. 198-200°, and a triacetyl-derivative, m.p. 204-6°, which on controlled hydrolysis leaves a. V-acetyl derivative, m.p. 177-180°. Aceording to Saito, veratramine on treatment with methyl iodide in methyl alcohol in presence of sodium carbonate, yields A-methylveratramine methiodide, m.p. 268° (dec.), from whieh the methoehloride, m.p. 277°, ean be prepared. 

In addition to simple halides, the method was used to prepare chol-esteryl iodide (30%) and cyclohexyl iodide (34%) from the corresponding alcohols, thus demonstrating the applicability of the reaction to cyclic secondary alcohols. An early adaptation to carbohydrates was reported by Lee and El Sawi (75). They claimed that treatment of l,2 5,6-di-0-isopropylidene-D-glucofuranose (49) with triphenylphosphite methiodide... 

The optically active iodide 153 (Scheme 43) can be conveniently prepared from commercially available methyl (S)-(+)-3-hydroxy-2-methylpropionate (154) (see Scheme 41). At this stage of the synthesis, our plan called for the conversion of 153 to a nucleophilic organometallic species, with the hope that the latter would combine with epoxide 152. As matters transpired, we found that the mixed higher order cuprate reagent derived from 153 reacts in the desired and expected way with epoxide 152, affording alcohol 180 in 88% yield this regioselective union creates the C12-C13 bond of rapamycin. 

For the corresponding bromides and iodides, preparation starts with K2PtX4 (X = Br, I) formed in situ from PtCl - with KX. For trans-Pd(PR3)2Cl2, shaking alcoholic PdCl2 or Na2PdCl4 with the phosphine yields a solution of the yellow complex. 

By the inteiaction of alcohols or glycols with potassium iodide and 95 per cent, orthophosphoric acid (the last named is prepared from the commercial 86 per cent, acid and phosphoric oxide), for example ... 

There are also useful procedures for preparation of azides directly from alcohols. Reaction of alcohols with 2-fluoro-l-methylpyridinium iodide followed by reaction with lithium azide gives good yields of alkyl azides.75... 

Ethyl fumarate has been prepared from fumaric acid and ethyl alcohol, with or without sulfuric acid as catalyst,4 from silver fumarate and ethyl iodide,5 from silver maleate and ethyl iodide plus a trace of iodine,6 from ethyl maleate by the action of iodine,6 from ethyl maleate and phosphorus pentachloride,7 and by passing hydrogen chloride into a boiling absolute alcohol solution of malic acid.8... 

Methyl pyruvate has been prepared from the silver salt of pyruvic acid and methyl iodide,3 and from the free acid by the alcohol-vapor method without a catalyst.4 Pyruvic esters have also been prepared by the dehydrogenation of lactic acid esters.5... 

Aside from alcohols, other oxygen nucleophiles have also participated in hydroalkoxylation reactions with alkynes. The most common of these are 1,3-dicarbonyl compounds, whose enol oxygens are readily available to add to alkynes. Cyclization reactions of this type have been carried out under Pd(0) catalysis with various aryl or vinyl iodides or triflates, often in the presence of CO, affording the corresponding furan derivatives (Equation (95)).337-340 A similar approach employing cyclic 1,3-diketones has also been reported to prepare THFs and dihydropyrans under Pd, Pt, or W catalysis.341 Simple l-alkyn-5-ones have also been isomerized to furans under the influence of Hg(OTf)2.342... 

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