S-lactones

Dihydropyrans have been produced by the 1,3 cycloaddition of methyl vinyl ketone (77) or acrolein (29-J7) with enamines (see Section II.A.2). S-Lactones have been formed as a side product in the reaction of dimethyl ketene with enamines (77), and as the primary products in the reaction of excess ketene with enamines derived from ketones (75) (see Section II.A.4). 

FIGURE 14.25 Catalytic antibodies are designed to specifically bind the transition-state intermediate in a chemical reaction, (a) The intramolecnlar hydrolysis of a hydroxy ester to yield as products a S-lactone and the alcohol phenol. Note the cyclic transition state, (b)... 

Increasing the molecular weight of polyester (or polyether) or changing its chemical composition could lower the Tg of the TPU and decrease the crystallinity of the polymer. For example, a TPU composed of poly(S-lactone), MDI, and 1,4-butanediol was found to have the lowest degree of crystallinity and, therefore, the best compatibility with PVC when the hard segment in it is 36% by weight [10]. 

Treatment of bicyclic lactones 66, derived from Diels-Alder reaction of 3-carboxy-2-pyrone under standard radical conditions using (TMSlsSiH, leads to bridged lactones 67, which can smoothly be converted to bicyclo[3.3.0]-lactones 68 (Scheme 10). For X = CHaOMe, this cascade of rearrangements took place in a 78% overall yield, providing 68 in diastereomerically pure form. Three additional steps provided a novel route toward Corey s lactone 69. 

As the WT CHMO was known to react (S) selectively with simple four-substituted cyclohexanone derivatives [84—87], it was logical to test mutant 1-K2-F5 as a catalyst in the BV reaction of other ketones. For example, when 4-methoxycyclohexanone (38) was subjected to the BV reaction catalyzed by mutant 1-K2-F5, almost complete enantioselectivity was observed in favor of the (S)-lactone (39) (98.5% ee), in contrast to the WT, which is considerably less selective (78% ee) (see Scheme 2.11) [89]. 

Inhibition of Glycosidases by AIdono-l,S-lactones and Aldohexoses Expressed by the Dissociation Constant K of the Enzyme-Inhibitor Complex... 

Similarly, methyl methacrylate reacts with ketones and TMSH/RuCE-SlEO to give /l-trimethylsiloxy-2,2-dimethyl methyl esters in good yields. A lactone example is shown in Eq. 292.473 Methyl acrylate, trans methyl ( )-cinnamate, and 3,4-dehydro-S-lactone react in an analogous manner, albeit in lower yields.473... 

A recent paper 26) also reported that the photo [2 + 2] reaction between the olefin (63) and the ester (56) would yield the desired photoadduct (64), which was then reduced by LiAlH4 to afford the diol (65). The diol (65), upon oxidation, gave the a-methylene-S-lactone (67) via the intermediate lactol (66) (Table 3)26). 

The reduction of Woodward s lactone with Saccharomyces cerevisiae produced an intermediate which is used for the preparation of hypotensive alkaloids (equation 44)118. 

P" and S-lactones present in the pheromone system of the giant white butterfly, Idea leuconoe, were synthesized. 

Preparation of spirocyclic ortho esters by the addition of epoxides to y- and S-lactones using BF3 or SnCl4 as catalyst [158, 159]. 

S-lactone (Note 1) is added slowly with vigorous stirring. During the addition, the temperature should be kept below 65°. After an hour in the ice bath, the solution is kept at room temperature for 24 hours and is then poured into 1 1. of water and stirred until the hydrolysis of the acetic anhydride is complete (about an hour). The mixture is placed in a refrigerator until the product crystallizes completely (Note 2). The crude material is removed by filtration and washed with a small amount of ice water. The 2,3,4,6-tetra-O-acetyl-D-gluconic acid monohydrate thus obtained melts at 113-117°. The yield is 79-84 g. (74-79%). 

Deprotonation of (S-lactones.1 Deprotonation of the 2-oxetanone (1) with LDA in THF at —78° generates 2, which is stable below room temperature. The anion reacts with electrophiles with high stereoselectivity at the fran.r-position at C3. The paper discusses reasons for the unexpected stability of 2. 

In the field of furocoumarins, which includes a large number of compounds extracted from the Umbelliferae, the nomenclature is rather uncertain. Up to 1968, those compounds were looked upon (Chemical Abstracts) as S-lactones of Bz-o-hydroxybenzofurylacrylic acids more recently, as furochromenic derivatives.10 Some of those compounds have names related to their geographical or botanical origin, such as sachalinin (7), recently extracted from the roots of Angelica sachalinensis 11 it is then advisable to add the chemical name. 

J. C. L6pez, A. M. G6mez, and S. Valverde, A novel entry to cyclohexanes and cyclopentanes from carbohydrates via inversion of radical reactivity in hex-2-enono-S-lactones, J Chem Soc., Chem. Commun. 613 (1992). 

It is difficult to identify the lipid moiety as a polyprenol, because of the small amounts present in tissues. Nevertheless, some information can be obtained by using glycosylated lipids labelled in the sugar moiety. The first indication of the presence of polyprenyl glycosyl phosphates comes from study of the properties just mentioned, namely, lability to mild acid, stability to mild alkali, and acidic properties. Information on the polyprenyl nature of the lipid may be obtained by labelling the lipid with radioactive 2,4-dideoxyO-C-methyl-D-g/ycero-pentono-l.S-lactone (mevalonic acid ). 

The cyclofunctionalization of 4-alkynoic and 5-alkynoic acids generates y-alkylidene-y-lactones and 5-alkylidene-S-lactones, respectively (equation 76 and Table 22). The initial products from the reactions catalyzed by mercury or silver salts undergo protiodemetallation under the reaction conditions. The vi-nylpalladium intermediates undergo either protiodemetallation or coupling with an added allyl halide. The palladium(II)-catalyzed cyclization of 3-alkynoic acids proceeds by 5-endo closure to give 3-buten-4-olides (Table 22, entry 2).50 190... 

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