Ester synthesis from white

The boronic esters (Chart 9) are easily hydrolyzed to the corresponding homoallylic alcohols using triethanolamine 98). Consequently, the allylboration sequence provides a synthesically useful alternative to the familiar Grignard synthesis of homoallylic alcohols. However, the protonolysis by triethanolamine causes a problem in the isolation of homoallylic alcohol from the thick, sticky, air sensitive boron-containing mixture. Fortunately, treatment of a pentane solution of borinate esters of 9-BBN with 1-equivalent of ethanolamine results in the rapid formation of a fluffy white... 

FIGURE 6.22 Shuttling of cholesterol from one type of cell to another. An HDL may pick up cholesterol from a macrophage, a white blood cell that phagocytizes debris in the bloodstream (e.g., dead red blood cells). A dead red blood cell contains cholesterol, since it contains a plasma membrane. (1) The macrophage can donate the cholesterol (that it has "eaten") to a passing HDL. (2) The cholesteryl ester that is formed is then transferred, in the circulation, to a VLDL. This transfer is catalyzed by an enzyme in the bloodstream called cholesteryl ester transfer protein (CETP). (3) Eventually, the cholesteryl ester can be delivered to the liver and excreted as a bile salt or (4) delivered to a cholesterol-needy cell. This ceU may be a premature red blood cell that is engaging in membrane synthesis and mitosis. 

Calvey, E.M., Matusik, J.E., White, K.D., DeOrazio, R., Sha, D. and Block, E. (1997) Allium chemistry supercritical fluid extraction and LC-APCI-MS of thiosulfinates and related compounds from homogenates of garlic, onion, and ramp. Identification in garlic and ramp and synthesis of 1-propanesulfinothioic acid S-allyl ester. J. Agric. Food Chem. 45(11) 4405-4413. 

White phosphorus in THF reacts in a long radical chain reaction with carbon radicals derived from Barton s PTOC esters. Oxidation of the adducts (HgOg or SOg) provides a convenient synthesis of phosphonic acids. For sensitive products the further transformation to phosphonic acids is best carried out with an excess of SO2. The reaction is illustrated by the synthesis of L-2-amino-4-phosphonobutyric acid in 58% yield from L-glutamic acid using the appropriate protecting groups (Scheme 8.91). ... 

CO2 is well known to react with primary and secondary amines. In fact the white solid often found on the mouth of bottles containing these amines is the carbamate salt (R2NCO2HNR2) formed from the CO2 in the air. This type of salt has been used to advantage in a carbapenam synthesis during the hydrogenolysis of a 4-nitrobenzyl ester. Prereduction of the Pd-C was necessary to prevent the formation of colloidal... 

White needed the diacid ester Z,E,Z-255 for his synthesis of the anti-leukaemia compound ver-rucarin.54 It must clearly be made from the components Z-256 and E,Z-251 though there are obvious selectivity problems in getting the right ester from compounds with three different C02H groups. 

The homoallylic acetal radical cyclization product reported by Stork [55] was later used in the construction of a significant portion of the gelsemine structure [76]. Further examples for homoallylic acetal cyclization exhibiting useful stereoselectivity include the (-)-protoemetinol synthesis by Fukumoto [77] and the rhizoxin partial syntheses by Rama Rao [78] and White [79]. In the synthesis of (+)-12b-epidevinylantirhine (117) [80] (Scheme 40), Ihara adopted low-temperature conditions for radical cyclization of the chiral unsaturated ester 114 in the presence of MAD. The lactone 116 in high diastereomeric excess was obtained from the cycli-... 

Synthesis of 2H,2H,3H,3H-Perfluoro-uiidecaiioic-acid-N-succinimidyl-ester. 2H,2H,3H, 3H-PerfIuoroundecanoic acid (1.354 g, 2.75 mmol, Fluorous Technologies Inc., Pittsburgh, PA), A-hydroxysuccinimide (348 mg, 3.02 mmol), and dicyclo-hexylcarbodiimide (622 mg, 3.02 mmol) were dissolved in ethyl acetate (120 mL) and stirred for 18 h at room temperature. The white precipitate formed (dicyclohexyl urea, DCU) was filtered off, and the remaining solution evaporated to dryness. The residue was recrystallized twice from ethyl acetate. Yield 1.00 g (62%), containing some traces of DCU. NMR (CDCI3, 300 MHz, ppm) 3.0 (m, 2H CH2), 2.88 (s, 4H CH2 NHS), 2.6 (m, 2H CH2). 

Synthesis of morphine esters, a) 3-Acetyl-d -morphine (I-e). Morphine base (50 mg) was dissolved in 2 ml acetic anhydride- e and remained at room temperature for 20 min. Water 5 ml) was added, and after the solution became homogenous, solid sodium carbonate was added to pH 8.5. The mixture was extracted with 3-20ml ether portions. The ether extracts were combined and evaporated to dryness. The product was eluted with 2% ethanol in benzene from 4.0 gram silica (adsorbosil-5) to give ( "e). b) 3-AcetyImorphine (I-b). Morphine base (50 mg) was treated with 2 ml acetic anhydride at room temperature for 20 minutes. 3-Ace ty Imorphine was isolated for mass analysis by the same procedure as (I-e). c) 6-Acetyl-ds--morphine (I-g). 3,6-Diacety 1- 3-morphine (50 mg) was converted to its hydrochloride with HCl (g) in anhydrous ether. The white precipitate was collected on a Buchner funnel. The product was then dissolved in 20 ml water and 0.1 gram hydroxylamine hydrochloride was added. After 2 minutes, solid sodium carbonate was added to pH 8.5 and the solution was extracted with 3-20 ml ether portions. 

In the synthesis depicted in Fig. 10, White et al (52) converted the protected methoxymethyl (MOM) ether (30) derived from (29) into the aldehyde (31), followed by a Wittig reaction to obtain the E a,P-unsaturated ester (32). Subsequent reaction of the bis-MOM derivative (33) with lithium diisopropylamide furnished, via a fragmentation-recombination process, two diastereoisomers (34) and (35). After chromatographic separation of (34), its bis-ether derivative (36) was converted into... 

A novel synthesis of (+)-mtegerrinecic acid lactone, the necic acid component of the macrolactone pyrrolizidine alkaloid integerrimine 53, has been reported by White and Jayasinghe, wherein lactonization of a 6-hydroxy acid was used for the ring closure [46] (Scheme 9). Reduction of epoxide 49 derived from / -(+)-P-citronellol and subsequent protection gave bis-3,5-DNB ester 50. Oxidative cleavage of the double bond afforded the carboxylic acid which upon saponification of the esters and acidification resulted in spontaneous lactonization to provide lactone 52. 

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