Wittig reaction butyllithium

The overall sequence of three steps may be called the Wittig reaction, or only the final step. Phosphonium salts are also prepared by addition of phosphines to Michael alkenes (hke 15-8) and in other ways. The phosphonium salts are most often converted to the ylids by treatment with a strong base such as butyllithium, sodium amide, sodium hydride, or a sodium alkoxide, though weaker bases can be used if... 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Olefination Reactions Involving Phosphonate Anions. An important complement to the Wittig reaction involves the reaction of phosphonate carbanions with carbonyl compounds 253 The alkylphosphonic acid esters are made by the reaction of an alkyl halide, preferably primary, with a phosphite ester. Phosphonate carbanions are generated by treating alkylphosphonate esters with a base such as sodium hydride, n-butyllithium, or sodium ethoxide. Alumina coated with KF or KOH has also found use as the base.254... 

Acetyl-3-bromofuran (1141) was prepared by Friedel-Crafts acylation of 3-bromofuran (1140). Wittig reaction of 1141 with methyltriphenylphosphonium bromide and butyllithium led to 3-bromo-2-propenylfuran (1142), which, on Sonogashira coupling with ethyl 2-ethynylphenylcarbamate (1143), provided N-protected (2-isopropenylfur-3-yl)ethynylaniline 1144. The TBAF-promoted... 

R. The use of butyllithium in tetrahydrofuran or ether-hexane affords the triene 1n only 50-60% yield. When the ylide was generated with sodium hydride or potassium tert-butoxide in dimethyl sulfoxide by the submitter, the Wittig reaction gave triene containing 10-20% of the Z isomer. Part C illustrates the selective hydroboration of a diene with disiamylborane.1 The reaction is best carried out by adding preformed disiamylborane to the triene. Lower yields of homogeraniol were obtained by the submitter when the triene was added to the borane reagent. 

Polyunsaturated aliphatic alkohols, aldehydes, ketones, and esters occur as fragrance components in fats, oils, fruits and plants 158). As an example the synthesis of ethyl (2 ,4Z)-2,4-decadienoate (232, pear ester ), which is responsible for the aroma of bartlett pears 161) is given. 2,4-Diunsaturated ester 232 may be obtained by a number of highly stereoselective syntheses, a lot of them making use of the Wittig reaction. Ohloff and Pawlak condensed 4,5-epoxy-( )-2-pentenal 228 with the ylide generated from 229 (butyllithium/ether) to the alkadiene epoxide 230 which was oxidized with periodic acid to the 2,4-decadienal 231. 231 is subsequently converted with MnOj/NaCN in ethanol to the pear ester 232162) [75 % (Z)-amount of the C-4 double bond] (Scheme 44). 

Wittig reactions are commonly used for the elaboration of side-chains. When l-methylimidazole-5-carbaldehyde is heated with iodomethyltriphenylphosphonium iodide, and the iodoethenyl product is treated with /z-butyllithium in THF, the ultimate product is the highly toxic 5-ethynyl-l-methylimidazole 616 (Scheme 131). 

Conia7 recommends this base as a substitute for the usually employed phenyllith-ium or n-butyllithium for preparation of nonstabilized phosphonium ylides. The base is soluble in various organic solvents and the /-amyl alcohol formed apparently improves the yields in the Wittig reaction. 

Triphenylphosphine, a white crystalline solid, is utilized widely in the Wittig reaction for olefin synthesis. This reaction involves-the-formation of alkylidenetriphenylphosphoranes from the action of butyllithium or other base on the quaternary halide, for example,... 

The silylated methyl ester was then a-methylated with lithium diisopropylamide and methyl iodide in tetrahydrofuran. Reduction of methyl 10-( erl-butyldimethylsilyloxy)-2-methyldecanoate with DIBAL in ether at -78°C afforded the corresponding aldehyde. The 10- tert-butyldimethylsilyloxy)-2-methyldecanal was subsequently coupled in a Wittig reaction with 1-hexyltriphenylphosphonium bromide and n-butyllithium affording (Z)- and ( )-1 -(teri-butyldimethylsilyloxy)-9-methyl-10-hexadecene in a 9 1 ratio, respectively. Deprotection with tetrabutylammonium fluroride (TBAF) in tetrahydrofuran and final oxidation with pyridinium dichromate (PDC) in dimethylformamide resulted in a 9 1 mixture of (Z)- and ( )-9-methyl-10-hexadecenoic acid as shown in Fig. (7). As was also the case with acid 6, the stereochemistry at C-9 in 7 is not known. The key step in the synthesis of the allylic methyl group was a-methylation of a methyl ester, followed by reduction to the corresponding aldehyde, which was used in the subsequent Wittig reaction. 

Some of the most profound lithium ion effects are observed in diethyl ether, benzene, or toluene, and the literature on Wittig reactions under these conditions contains a number of results that appear to be somewhat contradictory. The reason for this lack of consistency may be related to issues of lithium halide or betaine adduct solubility. Thus, Bergelson and Shemyakin et al. (5c, d) were able to show that ylide solutions prepared in benzene behaved differently if they were filtered to remove precipitated salts prior to use (compare Table 11, entries 3 and 4 entries 47 and 48). Later, it was shown that filtered toluene solutions of Ph3P=CHCH3 obtained from the phos-phonium bromide using butyllithium contain <0.1% bromide according to elemental analysis (18b). Therefore, the dramatic change in the alkene ratio... 

The presence of halogen atoms in a molecule is compatible with formation of an ylid and subsequent Wittig reaction. Carbon tetrabromide and triphenylphosphine have been used to give vinyl dibromide products, which are rapidly converted to the corresponding alkyne. Indeed, this is an important synthetic route to alkynes called the Corey-Fuchs procedure. The reaction of 511 with this reagent gave vinyl dibromide 512 in 77% yield as part of Marshall s synthesis of callystatin When 512 was treated with butyllithium... 

Modified Wittig reaction. The reaction of methylenetriphenylphosphorane (prepared in situ from methyltriphenylphosphonium bromide and -butyllithium) with the hydroxy ketone 1 in ether is markedly improved by addition of 3 equiv. of HMPT. As the reaction proceeds, a complex of LiBr and HMPT separates from the ether solution. Probably the Wittig reaction becomes salt free, with enhancement of the rate and increase in yield from 24 to 66%. The product (2) is converted by hydrogenation into er> //rro-3,7-dimethylpentadecane-2-ol, esters of which are sex attractants of pine saw flies. ... 

The (S)-lactone acid 1, obtained from L-glutamic acid by nitrous acid deamination, was converted to the acid chloride, then treated with excess diazomethane followed by hydrogen iodide to yield the keto-lactone 2. Amidation occurred quantitatively to give the partially racemized amide 3, which was purified by repeated recrystallizations. The vicinal diol resulting from reaction with excess methylmagnesium iodide was protected as the acetonide 4. An isomeric mixture of olefins (Z , 26 74) was obtained from the subsequent Wittig reaction. Reduction followed by separation on silver nitrate coated silica gel gave the (Z)-and ( )-alcohols in 20% (6) and 61% (5) yield, respectively. Conversion of the (S)-( )-alcohol (5) to the chloride then afforded the thioether (7) on reaction with sodium phenylsulfide. The thio ether anion was formed by treatment with n-butyllithium. Alkylation with the allylic chloride" (8), followed by removal of sulfur, then yielded the diene 9, which was converted in several steps to (/ ) (-t-)-10,11 -epoxy famesol. 

E3VC can be prepared by the Wittig reaction of 9-ethyl-3-carbazolecarboxaldehyde in THF. This monomer can be anionically polymerized using n-butyllithium as an initiator. Further, a block copolymer with styrene can be prepared. The polymers exhibit a blue photoluminescence [56]. 

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