2-Hydroxy-2-methylpropanic acid

The stereochemistry was controlled by Lewis acid-induced addition of these allylic silanes to aldehydes. The reaction of the silane with O-protected (S)-3-hydroxy-2-methylpropanal provides 15. The silane reacted with the benzyl-protected analog to provide 16. 

Stereoselective Aldol Reactions. The (R)- and (S)-2-hydroxy-1,2,2-triphenylethyl acetates (HYTRA) offer a simple soludon for a stereoselecdve aldol addition of a-unsubstituted enolates. When a suspension of HYTRA is treated in THF with 2 equiv of Lithium Diisopropylamide, a clear soludon of the enolate forms (eq 1). Subsequent dilution with 2-methylbutane followed by the addition of 2-methylpropanal affords predominantly the (R,R)-diastereomeric adduct. Alkaline hydrolysis not only delivers (/ )-3-hydroxy-4-methylpentanoic acid in 86-94% ee but also liberates the optically pure auxiliary reagent (/ )-1,2,2-triphenylethane-1,2-diol, which can be removed and reused (eq 1). - ... 

In a second investigation, racemic 2-hydroxy-4-phenylbutanoic acid (42) was reacted with lipase PS (LPS) and vinyl acetate (VA) (ethenyl ethanoate) in /-butyl methyl ether (2-methoxy-2-methylpropane) to give acetate (S)-43 in 35% yield and in 99% ee unreacted alcohol 44 was found to have 99% ee with R configuration predominant (Scheme 3.3). 

HIBA 2-Hydroxyisobutyric acid HIBAL 2-Hydroxy-2-methylpropanal HRT Hydraulic retention time LUST Leaking underground storage tank MBR Membrane bioreactor MTBE Methyl tert-butyl ether MPD 2-methyl 1,2-propanediol N Nitrate NA Natural attenuation ND Not determined ns Not specified P Phosphate... 

Using the same procedure, l-hydroxy-2-amino-2-methylpropane-l,l-diphosphonic acid and 2 -pyrroIidine-l-hydroxymethane-l,l-diphosphonic acid were obtained (ref. U.S. Pat. 4,267,108, 1981). 

Although there are a number of syntheses of pantothenic acid, that of Folkers et al. is among the earliest. As shown in Scheme 12.108, a clean synthesis of a-hydroxy-P,P-dimethyl-Y-butyrolactone was needed. First, 2-methylpropanal (isobutyraldehyde) underwent an aldol condensation with formaldehyde (formalin, H2C=0) to produce a,a-dimethyl-P-hydroxypropanal. Then, the bisulfite adduct of this aldehyde underwent reaction with potassium cyanide (KCN) and the separated cyanohydrin was hydrolyzed with concentrated hydrochloric acid (HCI), and the product was carefully made basic. The racemic a-hydroxy-P,P-dimethyl-y-butyrolactone was separated, while the lactone underwent ring opening in the... 

Chang et al. [73] and Nawar et al. [74] have identified many of the volatiles formed during deep fat frying. They have found numerous acids, alcohols, aldehydes, hydrocarbons, ketones, lactones, esters, aromatics, and a few miscellaneous compounds (e.g., pentylfuran and 1,4-dioxane) as products of deep fat frying. More recently, Wagner and Grosch [75] have studied the key contributors to French fry aroma. The list of key aroma compounds in French fries includes 2-ethyl-3,5-dimethylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-isobutyl-2-methoxypyrazine, (E,Z), (E,E)-2,4-decadienal, trans-4,5-epoxy-(E)-2-decenal, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, methylpropanal, 2- and 3-methylbutanal, and methanethiol. If one examines this list, it is obvious that the Maillard reaction (pyrazines, branched chain aldeydes, furanones, and methional), and lipid oxidation (nnsaturated aldehydes) are the primary sources of this characteristic aroma. 

The p-hydroxycarbonyl or aldol system, present in the 3-hydroxy-4-methyl-pentanoyl group of the hydrated ailo-isohumulones, may undergo a retro-aldol reaction (Fig. 58) (13), giving acetyihumulinic acids together with 2-methylpropanal. The very pungent odour of this aldehyde is always observed when carrying out isomerizations of humulone. 

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