B-Lactone

Nach Umkristallisieren aus Hcxan/Essigsaure-athylester wird das b-Lacton gebildet F 136-137°. 

B. Lactones. The crude mixture of rac-3 and rac-4 is dissolved in 300 mL of dry methanol (distilled from sodium) containing 10 drops of coned hydrochloric acid and heated under reflux for about 8 hr until the reactants can no longer be detected by thin layer chromatography (Note 6). The solvent is removed on a rotary evaporator at 25°C and the remaining residue, which consists of an 8 1 mixture of lactone rac-5 and dimethyl ester rac-6 is dissolved in dry dichloromethane (50 mL). The solution is acidified with trifluoroacetic acid (10 mL) and stirred at room temperature for about 48 hr, until the thin layer chromatogram does not show any dimethyl ester rac-6 (Note 6). The organic layer is washed with water (50 mL), saturated sodium bicarbonate solution (2 x 50 mL), water (50 mL), and brine (50 mL), dried over sodium sulfate,... 

Barnett and Sohn (12, 13, see also 14) have discovered that the iodolactoni-zation of b,r-unsaturated carboxylic acid salts 37 yield, under kinetically controlled conditions, the Y-iodo-B-lactones 39 in preference to the more stable B-iodo-Y-lactones l. Similar results were obtained in the course of the bromolactonization reaction. Thus, here again, the formation of a four-membered ring is more facile than that of a five-membered ring. This can be rationalized on the basis of Stork s analysis, i.e. the internal opening by the carboxylate anion of the three-membered ring iodonium ion (or bromonium) 38 39 is preferred over the other mode of opening 40 41 for stereoelectronic reason. 

Water-saturated phenol—1% ammonia—hydrocyanic acid.87 2. Water-saturated s-collidine,27 3. 1-Butanol-acetic acid—water 4 1 5 v/v.87 4. Ethyl acetate-pyridine-water 2 1 2,28 5. Ethyl acetate—acetic acid—water 3 1 3.6. feri-Pentyl alcohol—1-propanol—water 4 1 1.5.108 b Lactone. Free base. 

FIGURE 2.32 Significant oxygen surface groups on a carbon surface (a) carboxyl, (b) lactone, (c) carbonyl, (d) ether, (e) pyrone, (f) phenol, and (g) carboxyl anhydride. 

This methodology has been expanded to geranyl methyl carbonate for the synthesis of the vitamin E nucleus, and to tiglyl methyl carbonate for the synthesis of (—)-calanolide A and B. In the latter example, the anthracenyldiamine -based ligand was required for optimum selectivity. The synthesis of (—)-aflatoxin B lactone utilizes a dynamic kinetic asymmetric transformation, whereby a suitably functionalized phenol reacts with a racemic 5-acyloxy-2-(5//)-furanone to provide a single product in 89% yield. One final example of phenol as a nucleophile is for the deracemization of Baylis-Hillman adducts." ... 

C5H603 4,5-epoxy-3-hydroxyvaleric acid b-lactone 4247-30-7 503.33 44.204 2 4683 C5H7N02 glutarimide 1121-89-7 477.25 41.703 2... 

As stated above. It has been established that carboxylate Ions are the true Initiators in B lactone polymerization. In an early study. Hall ( ) stated that In Intermediate pH ranges anions or water Itself attack the CH2 group with alkyl-oxygen cleavage by SN2 reaction that proceeds most rapidly In anhydrous acetonitrile or tetrahydrofuran. From heats of combustion he determined the heat of polymerization of plvalolactone AH j. to be -20.1 kcal mol l. 

Because the heat of polymerization Is high. Hall was able to use a calorimetric method (10,11) to determine polymerization rates. The process can be described by Initiator I attacking the B-lactone M to give the B substltuted carboxylate IM, which attacks additional monomer molecules to give the poly-B-lactone IM2 In those cases when kp Is only slightly less than kj, the... 

Inasmuch as the polymerization of B lactones, and plvalo-lactone In particular. Is very rapid, the question arises as to how... 

Helical conformations with two monomer units per turn appear to be general for polymers from B lactones.(18) Fiber repeat distances may vary, but not by a great amount. Examples are polyproplolactone and poly(D,L-or-methyl-a-n-propyl-B-proplolactone). Both are converted to a planar zig-zag form by stretching and both reverts to a helical configuration upon annealing. 

Scheme 5.42. Sulfoxide mediated asymmetric Michael additions to (a) cycloalkenones and (b) lactones. Both are postulated to proceed via the nonchelate model. Figure 5.1 lb [210].

Wegen der vcrmuteten Bildung ernes mtermediaren b-Lactons Ia8t si eh die Kondcnsation von Propylidcn-malonsaure-dimethylester mit aromatischen Aldehyden zu (3-Aryl-2-methyl-2-propenyliden)-malonsaure-methylester als Variante der Stobbe-Kondensation auffassen812 ... 

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