Lactones epoxide ring opening

Other synthetically useful intramolecular epoxide ring openings have been reported. For example, the strained methylene epoxide 79, derived from DMD epoxidation of the corresponding allene 78, undergoes spontaneous isomerization to the lactone 81 via attack of the... 

Feldman has reported two interesting exeunples of epoxide ring opening. The opening reaction in the epoxides (34a) and (34b) affords an ylide-like species that is intramolecularly trapped to yield the two adducts (35a) and (35b). The 3-substituted derivative (34b) also affords another product identified as (36). The formation of this product is thought to involve a Norrish Type I process proceeding via (37) to the lactone (38) which then undergoes [2-1-2] cycloaddition. 

Tetradecyl oxirane is reacted with diethyl acetamidomalonate in basic medium. The presence of LiCl, co-impregnated with KF on alumina, is necessary here to insure the electrophilic assistance to ring opening. The main product is a lactone, formed after epoxide ring opening and subsequent cyclization [Eq. (75)]. 

A similar transformation can be carried out under milder conditions by taking advantage of silyl ketene acetals, a masked form of the earboxylate dianion. When epichlorohydrin 53 was treated with the ketene acetal 79 in the presence of titanium(IV) chloride, a regioseleetive epoxide ring opening occurs at the less substituted carbon. Treatment of the crude reaction mixture with catalytic p-toluenesulfonic acid promoted a lactonization to the y-butanolide 80 in high overall yield <04T8957>. 

Active methylenes also react with epoxides in the presence of aluminum oxide, lithium chloride and potassium fluoride under microwave for 5 min (Abenhdim et al., 1994). The main product is a lactone formed by epoxide ring opening followed by cyclization. 

Epoxides provide another useful a -synthon. Nucleophilic ring opening with dianions of carboxylic acids (P.L. Creger, 1972) leads to y-hydroxy carboxylic acids or y-lactones. Addition of imidoester anions to epoxides yields y-hydroxyaldehyde derivatives after reduction (H.W. Adickes, 1969). 

The stereochemistry of ring-opening polymerizations has been studied for epoxides, episul-fides, lactones, cycloalkenes (Sec. 8-6a), and other cyclic monomers [Pasquon et al., 1989 Tsuruta and Kawakami, 1989]. Epoxides have been studied more than any other type of monomer. A chiral cyclic monomer such as propylene oxide is capable of yielding stereoregular polymers. Polymerization of either of the two pure enantiomers yields the isotactic polymer when the reaction proceeds in a regioselective manner with bond cleavage at bond 1. 

The stereochemistry of ring-opening polymerizations of episulfides, lactones, lactides, IV-carboxy-a-amino acid anhydrides, and other monomers has been studied but not as extensively as the epoxides [Boucard et al., 2001 Chatani et al., 1979 Duda and Penczek, 2001 Elias et al., 1975 Guerin et al., 1980 Hall and Padias, 2003 Imanishi and Hashimoto, 1979 Inoue, 1976 Ovitt and Coates, 2000 Spassky et al., 1978 Zhang et al., 1990]. 

Tsuruta, T. and Y. Kawakami, Anionic Ring-Opening Polymerization Stereospecificity for Epoxides, Episulfides and Lactones, Chap. 33 in Comprehensive Polymer Science, Vol. 3, G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, eds., Pergamon Press, Oxford, 1989. 

A second approach (472) to 512 started with trans-2-buitnc epoxide (524) (Scheme 67). Opening of the epoxide ring of 524 with lithium acetylide gave an acetylenic alcohol, which was converted to the acetylenic acid (525) by carbox-ylation with gaseous carbon dioxide. Partial hydrogenation of 525 followed by lactonization afforded the a,3-unsaturated lactone (526) which was transformed to the nitrolactone (527) by a Michael addition reaction of nitromethane. The Nef reaction of 527 gave the tetrahydrofuranyl acetal (528) which was converted to... 

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