2,6-Dimethylphenyl propionate

For the propionate aldol reaction the Li enolate (7), generated by deprotonation of 2,6-dimethylphenyl propionate with Lithium Diisopropylamide in EtiO, was chosen. Transmetalation with 1.25 equiv of an ethereal solution of (1) takes 24 h at —78 °C. The completion of this step is evident by the disappearance of racemic anti-a do (9) in favor of optically active yw-isomer (10) (91-98% ee) upon reaction with an aldehyde (RCHO) and aqueous workup. At this point, 3-11% of anri-aldol (9) remaining in the reaction mixture is optically active as well (eq 2). This awri-isomer (9) (94-98% ee) becomes the major product if the reaction mixture, containing the putative ( )-titanium enolate derived from (7), is warmed for 4-5 h to —30°C before reaction with an aldehyde (RCHO) again at —78 °C. Isomerization to the (Z)-titanium enolate is a possible explanation of this behavior. Some substrates, aromatic and unsaturated aldehydes, behave exceptionally, as a high proportion of yn-isomer (10) (19-77%) of lower optical purity (47-66% ee) is formed in addition to (9) (94-98% ee). After hydrolysis of the acetonide (6) the products (9/10) are isolated and separated by chromatography in 50-87% yield. The reactions of pivalaldehyde (R = r-Bu) are sluggish at —78°C and have therefore been carried out at —50 to —30°C. 

Dimethylphenyl propionate, 162 Dimethy Iphcnylsilyllithium, 162-163 Dimethyl(phenylthio)aluminum, 163-164 Dimethyl(phenylthiomethyl) amine, 164 Dimethylsulfonium ethoxycarbonylmethyl-... 

Deprotonation of 2,6-dimethylphenyl propionate gives the f(9)-enolate, which is transmetalated slowly to the titanium enolate at -78° [106]. Addition to a... 

The situation becomes a little more complex if the aldehyde contains a chiral centre, as in 2-phenylpropanal. In such cases, the aldol product formed contains three chiral centres and there are four possible diastereoisomers - two 2,3-syn and two 2,3-anti isomers (and their enantiomeric pairs, thereby totalling eight stereoisomers) (1.69). The relative stereochemistry of the substituents at C-2 and C-3 is controlled by the geometry of the enolate. The C-3,C-4 stereochemistry, on the other hand, depends on the direction of approach of the enolate and the carbonyl group to each other. This is illustrated in Scheme 1.70, for the reaction of 2-phenylpropanal with the trans-enolate of 2,6-dimethylphenyl propionate. 

Related Reagents. 3-(2-Benzyloxyacetyl)thiazolidine-2-thione 2,6-Dimethylphenyl Propionate 2-Methyl-2-(trimethyl-silyloxy)-3-pentanone l,3-Thiazolidine-2-thione Tin(II) Tri-fluoromethanesulfonate. 

Related Reagents. (S)-4-Benzyl-2-oxazolidinone 10,2-Camphorsultam (/ )-(+)-f-Butyl 2-(p-Tolylsulfinyl)propionate 10-Dicyclohexylsulfonamidoisobomeol Diisopinocampheyl-boron Trifluoromethanesulfonate (R,R)-2,5-Dimethylborolane 2,6-Dimethylphenyl Propionate Ethyl 2-(Methyldiphenylsilyl)-propanoate a-Methyltoluene-2,a-sultam 3-Propionylthiazoli-dine-2-thione (/ ,/ )-1,2-Diphenyl-1,2-diaminoethane iV,iV -Bis-[3,5-bis(trifluoromethyl)benzenesulfonamide] 1,1,2-Triphenyl-1,2-ethanediol. 

Duthaler and cosvorkers also reported asymmetric syn aldol methodology based on their titanium complex 146 [52]. Heathcock demonstrated the capacity of 2,6-dimethylphenyl propionate-derived lithium enolates to undergo addition to a range of aldehydes affording racemic anti aldol adduct 151... 

Preparation by Fries rearrangement of 2,6-dimethylphenyl propionate with titanium tetrachloride at 100° for 2 h (20%) [6981],... 

Also obtained by reaction of sec-butyllithium (1.1 equiv) with 2-bromo-4,6-dimethylphenyl propionate in tetrahydrofuran/ethyl ether/hexane at -95° for 30 min and -78° for 30 min, then hydrolysis with saturated ammonium chloride (31%) (Metal-promoted Fries rearrangement) [6590]. 

Also obtained by reaction of 2-bromo-4,6-dimethylphenyl propionate at low temperature (-78 to -95°) with sec-butyllithium to give, after hydrolysis, the titled ketone (metal-promoted Fries rearrangement) (yields 31% by GC 17% isolated) [6590],... 

UVA 2-hydroxy-4-octyloxybenzophenone 2-hydroxy-4-methoxybenzophenone 2-(2H-benzotriazol-2-yl)-p-cresol 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetraethylbutyl)phenol 2,4-di-tert-butyl-6-(5-chloro-2H-benzotriazole-2-yl)-phenol 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octyloxy) phenol ethyl-2-cyano-3,3-diphenylacrylate HAS 1,3,5-tri-azine-2,4,6-triamine, N,N [1,2-ethane-diyl-bis[[[4,6-bis[butyl-(1,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl] imino]-3,1 -propanediyi] bis[N ,N -dibutyl-N ,N -bis(1,2,2,6,6-pentamethyl-4-piperidinyl)- bis(2,2,6,6-tetramethyl-4-piper-idyl) sebacate 2,2,6,6-tetramethyl-4-piperidinyl stearate N,N -bisformyl-N,N -bis-(2,2,6,6-tetramethyl-4-piperidinyl)-hexamethylendiamine alkenes, C20-24-.alpha.-, polymers with maleic anhydride, reaction products with 2,2,6,6-tet-ramethyl-4-piperidinamine 1,6-hexanediamine, N, N -bis(2,2,6,6-tetramethyl-4-piperidinyl)-, polymers with 2,4-di-ohloro-6-(4-morpholinyl)-1,3,5-triazine 1,6-hexanediamine, N,N -bis(2,2,6,6-tetramethyl-4-piperidinyl)-, polymers with morpholine-2,4,6-trichloro-1,3,5-triazine reaction products, methylated Phenolic antioxidants ethylene-bis(oxyethylene)-bis(3-(5-tert-butyl-4-hydroxy-m-tolyl)-propionate) 2,6,-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5,-triazine-2-ylamino) phenol pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate) 2-(1,1 -dimethylethyl)-6-[[3-(1,1 -dimethylethyl)-2-hydroxy-5-methylphenyl] methyl-4-methylphenyl acrylate isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate 2,2 -ethylidenebis (4,6-di-tert-butylphenol) 2,2 -methylenebis(4-ethyl-6-tertbutylphenol) 3,5-bis(1,1-dimethyethyl)-4-hydroxy-benzenepropanoic acid, C13-15 alkyl esters phenol, 4-methyl-, reaction products with dicyclopen-tadiene and isobutene Phosphite trinonylphenol phosphite isodecyl diphenyl phosphite... 

UVA 2,4-dihydroxybenzophenone 2-(2H-ben-zotriazol-2-yl)-p-cresol phenol, 2-(5-chloro-2H-benzotriazole-2-yl)-6-(1,1 -dimethylethyl)-4-methyl- 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetraethylbutyl)phenol 2-(2H-benzotriazol-2-yl)-4,6-bis(1 -methyl-1 -phenylethyl)phenol 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol, branched linear 2,4-di-tert-butyl-6-(5-chloro-2H-benzotriazole-2-yl)-phenol reaction product of methyl 3(3-(2H-benzotriazole-2-yl)-5-t-butyl-4-hydroxyphenyl propionate/PEG 300 2-[4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(octyloxy) phenol (2-ethylhexyl)-2-cyano-3,3-diphenylacrylate HAS ... 

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