Lithium chlorochromate

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Scheme 10. Synthesis of the ds-donor-acceptor-substituted TEE 86 [ 100]. DIBAL-H diisobutylaluminum hydride, PCC pyridinium chlorochromate, LDA lithium diisopropylamide...

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

BASF AG CRBPII dba DBN DBU DIBAL-H DMAP DMF DMF-DMA DMPU HMDS HMPA HMPT H-LR LDA LDE LRAT MCPBA MOM NMO NMP PCC PhH = Badische Anilin- Soda Fabrik AG = cellular retinol-binding protein type II r dibenzylideneacetone = 1,5-diazabicyclo[4.3.0]non-5-ene = l,8-diazabicyclo[5.4.0]undec-7-ene = diisobutylaluminium hydride = 4-dimethylaminopyridine = A V-dimethylformamide = A,V-dimethylformamide, dimethylacetal = 1,3 -dimethyl-3,4,5,6-tetrahydro-2( 1H)-pyrimidone = hexamethyldisilazane = hexamethylphosphoramide = hexamethylphosphorous triamide = Hoffmann-La Roche = lithium diisopropylamide = lithium diethylamide = lecithin retinol acyltransferase = m-chloroperbenzoic acid = methoxymethyl = iV-methylmorpholine oxide = l-methyl-2-pyrrolidinone = pyridinium chlorochromate = benzene... 

Potassium hydroxide, 258 Trimethylsilyl chlorochromate, 327 of carbon-carbon double bonds substituted by heteroatoms m-Chloroperbenzoic acid, 76 of oximes to carbonyl compounds Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Titanium(III) chloride-Diisobutylalu-minum hydride, 303 Trimethylsilyl chlorochromate, 327 of protected alcohols Chlorodimethylthexylsilane, 74 Formic acid, 137 p-Methoxyphenol, 181 of thioacetals and -ketals Methoxy(phenylthio)trimethyl-silylmethane, 182... 

Lithium aluminum hydride-Hexa-methylphosphoric triamide, 159 Methoxyamine, 177 Titanium(III) chloride-Diisobutyl-aluminum hydride, 303 Trimethylsilyl chlorochromate, 327 From vinylsilanes m-Chloroperbenzoic acid, 76 Miscellaneous methods to prepare ketones... 

Chemicals AIBN CAN DIBAL DMAP DMSO HMPA LAH LDA mCPBA NBS NCS or PCC PDC Py TBAF TEMPO a.a -azobislisobutyronitrile) cerium(IV) ammonium nitrate diisobutylaluminium hydride 4-(dimethylamino)pyridine dimethyl sulfoxide hexamethylphosphoramide lithium aluminum hydride lithium diisopropylamide m-chloroperoxybenzoic acid A-bromosuccinimide A-chlorosuccinimide superoxide anion radical pyridinium chlorochromate pyridinium dichromate pyridine tetrabutylammonium fluoride 2,2,6,6-tetramethyl-l-piperidinyloxy free radical... 

Following the procedure for the transformation of acetate (12) to (16), the acetate (13) was converted to trans-acetate (18). Reduction of (18) with metal hydride followed by oxidation of the resulting alcohol with pyridinum chlorochromate produced ketone (11), which afforded alcohol (17) by reduction with lithium aluminium hydride. 

Fmoc HMPA Ipc KHMDS LDA MCPBA MEM Mes MOM MS- NBS NCS NIS (+)-NLE PCC PDC Ph3P Pht PMB PNB europium 9-fluorenylmethoxycarbonyl hexamethylphosphoric triamide isopinocamphenyl potassium hexamethyldisilazanide lithium diisopropylamide 3- chloroperoxybenzoic acid (2-methoxyethoxy)methyl mesityl methoxymethyl molecular sieves iV-bromosuccinimide iV-chlorosuccinimide iV-iodosuccinimide positive non linear effect pyridinium chlorochromate pyridinium dichromate triphenylphosphane phthaloyl 4- methoxyphenyl 4-nitrobenzyl... 

Lithium Di-iso propyl Amide Di-lsoButylALuminium hydride Pyridinium ChloroChromate Di Ethyl Azo-Dicarboxyl ate... 

Lithium DI-lsopropylAmIde DI-lsoButylALumlnlumhydrIde Pyridinlum ChloroChromate DIEthyl Azo-DIcarboxylate... 

If the reaction takes place via an anion or in a S 2 fashion, high yields of the product alkyl-cyclopropanes have been obtained. Thus, reaction of methyl 4,6-( -benzyIidene-2,3-dideoxy-2,3-C-[(7 )-(chloromethyl)ethylidene]-a-D-mannopyranoside (1) with lithium aluminum hydride in refluxing tetrahydrofuran gave methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-C-isopropylidene-a-D-mannopyranoside (2) in 89% yield. Similarly, treatment of chloromethylcyclopropane 3 with lithium triethylborohydride, followed by oxidation with pyridinium chlorochromate,. gave ishwarone (4) in 75% yield. ... 

However, this sequence can be reversed. - Thus, the activated cyclopropane can be de-protonated by lithium diisopropylamide, reacted with an appropriate ketone and opened by various methods such as treatment with acid or desilylation with fluoride. Using this reaction sequence, y-lactones 52 with various substituents can be obtained by the intramolecular attack of the ketone oxygen on the siloxy-substituted carbon followed by oxidation with pyridinium chlorochromate. The cyclic hemiacetal intermediates 53 can be converted to the tetrahyd-rofuran derivatives 55 by deoxygenation with triethylsilane/boron trifluoride. 

The synthetic utility of a-silyl esters has been amply demonstrated by several examples. The basis for this chemistry is the observation that ester lithium enolates can be directly C-silylated with methyldiphenylchlorosilane, a reagent which avoids the more common O-silylation153. The a-silyl-y-valerolactone 80 was converted in two steps and high yield to racemic ancepsenolide by condensation of its lithium enolate with decane 1,10-dicarboxaldehyde followed by isomerization to the endocyclic double bonds of the natural product154 (equation 160). Treatment of the a-silyl-y-butyrolactone 81 or 80 with a Grignard reagent followed by pyridinium chlorochromate (PCC) oxidation provides 4-oxo aldehydes and 1,4-diketones, respectively155 (equation 161). 

The reported synthesis for (5Z,9Z)-14-methylpentadeca-5,9-dienoic acid (14) started with commercially available 4-methylpentan-l-ol, which upon reaction with phosphorous tribromide afforded l-bromo-4-methylpentane [52], Commercially available pent-4-yn-l-ol was also protected as the tetrahydropyranyl ether as shown in Fig. (18). Formation of the lithium acetylide with n-BuLi in THF and subsequent addition of 1-bromo-4-methylpentane in hexamethylphosphoric acid triamide resulted in the isolation of the tetrahydropyranyl protected 9-methyldec-4-yn-l-ol. Hydrogenation of the alkyne with Lindlar s catalyst and quinoline in dry hexane afforded the cis hydropyranyl-protected 9-methyldec-4-en-l-ol. Deprotection of the alcohol with />-toluenesulfonic acid afforded (Z)-9-methyldec-4-en-l-ol. Pyridinium chlorochromate oxidation of the alcohol resulted in the isolation of the labile (Z)-9-methyldec-4-enal. Final Wittig reaction with (4-carboxybutyl) triphenylphosphonium bromide in THF/DMSO resulted in the desired (5Z,9Z)-14-methylpentadeca-5,9-dienoic acid (14). 

---