Medium Ring Lactones Research Articles

Enzymatic Resolution of Medium-Ring Lactones. Synthesis of (S)-(+)-Phoracantholide I

The horse liver and pig liver esterase hydrolysis of racemic medium ring lactones gives with excellent enantiomeric excess the S- (or R) lactones and the corresponding R- (or S) hydroxy acids. This is the first general method to obtain optically pure medium ring lactones. Application to the preparation of (S)-(+)-Phoracantholide I is reported.

Hypervalent Organoiodine-Promoted Oxidative Ring Expansions of Tributylstannyl Lactols. New and General Synthesis of Unsaturated Medium-Ring Lactones

Abstract A new ring expansion route to olefinic lactones was developed. Oxidative 1,4-fragmentation of tributylstannyl lactols utilizing (diacetoxyiodo)bezene under mild conditions gave unsaturated medium-ring lactones stereospecifically in good yields. The relative stereochemistry of tributylstannyl group of the lactols determines the double bond geometry of the lactones.

New general synthesis of medium ring-lactones [formula omitted] a regioselective β-scission of alkoxyl radicals generated from catacondensed lactols

We describe a new general method for the synthesis of medium-sized lactones based on ring-enlargement via a regioselective β-scission of alkoxyl radicals generated by photolysis from the hypoiodites of several catacondensed lactols. The syntheses of 9-membered lactones from 6 5 fused lactols, 10-membered lactones including a naturally occurring lactone, phoracantholide I, from 6 6 or 7 5 fused lactols, and 11-membered lactones from 7 6 or 8 5 fused lactols are shown to be achieved by the present method. This new method may have a potential for application to the synthesis of either smaller or larger-sized lactones.

Synthesis with 1,2-oxazines. 3. Reactions of .alpha.-chloroaldonitrones with enol ethers: a synthetic route to medium-ring lactones

Synthesis with 1,2-oxazines. 3. Reactions of .alpha.-chloroaldonitrones with enol ethers: a synthetic route to medium-ring lactones

Strain effects in acyl transfer reactions. Part III. Hydroxide and buffer-catalysed hydrolysis of small and medium ring lactones

Second-order rate constants for the alkaline hydrolyses of lactones and esters at 319 K decrease in the order methyl formate > δ-valerolactone > β-propiolactone > γ-butyrolactone, Iµ-caprolactone > methyl acetate. The enhanced reactivity of the δ-lactone is due to a reduction in enthalpy of activation but the β-lactone derives its extra reactivity solely from a favourable increase in the entropy of activation for BAC2 hydrolysis. Only the β-lactone exhibits detectable activity towards either pyridine or 1-methylimidazole in aqueous solution. For both amines, nucleophilic substitution with alkyl oxygen fission proceeds faster than attack at the acyl centre and results in the formation of a betaine as the major product. No reactivity could be detected for either amine with methyl formate or δ-valerolactone. It thus appears that conformational orientation factors are capable of accelerating the reaction of the ester group with strong nucleophiles whereas angle-strain effects become more important for weaker ones.