Triene lactones

Figure 2 (a) Classic biosynthesis of monensin A (7) (b) novel monensins (16) (c) monensinyl N-acetylcysteamine thioester (14) (d) triene lactones... 

R.S. Coleman and co-workers have developed a stereoselective synthesis of the 12-membered diene and triene lactones characteristic of the antitumor agent oximidines I and II, based on an intramolecular Castm-Stephens coupling. The effectiveness of this protocol rivals the efficiency of standard macrolactonization. The stereoselective reduction of the internai alkyne afforded the 12-membered ( ,Z)-diene lactone in good yield. 

When the lactone silyl ketene acetal 18-1 is heated to 135° C a mixture of four stereoisomers is obtained. Although the maj or one is the expected [3,3] -sigmatropic rearrangement product, lesser amounts of other possible C(4a) and C(5) epimers are also formed. When the reaction mixture is heated to 100° C, partial conversion to the same mixture of stereoisomers is observed, but most of the product at this temperature is an acyclic triene ester. Suggest a structure for the triene ester and show how it can be formed. Discuss the significance of the observation of the triene ester for the lack of complete stereospecificity in the rearrangement. 

In parallel investigations, Danishefsky and coworkers accomplished the preparation of the 16-membered lactone of a model epothilone system via an alternative C9,C10 disconnection [14] (Scheme 4). In this case, coupling of epoxy-alcohol 17 with acids 18a and 18b afforded trienes 19a and 19b respectively. RCM of 19a under the influence of ruthenium initiator 3 produced dienes 20a as a 1 1 mixture of Z -isomers. Under identical conditions, cyclization of 19b produced a single product 20b (tentatively assigned as the Z-isomer). The variable stereoselectivity observed in these reactions was inconsequential since the olefinic functionality could be reduced to afford the corresponding saturated macrolactones. Schrock s molybdenum initiator 1 promoted the cyclization of 19a and 19b with similar efficacy [14]. 

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

An unidentified Japanese species of the same genus yielded several cembranoids (75-78), all having seven-membered lactone systems. Their structures were elucidated based on spectral data and chemical correlations." Several other seven-membered cembranoid lactones, (l , 3 , 85, llZ)-4,8-dimethyl-1-isopropyl-7-oxo-cyclotetradeca-l,3,ll-triene and its IR and TS -hydroxyderivative (79-82), were isolated from an Australian species (Figure 6-7)." ... 

HYDROXYOCTANOIC ACID LACTONE see OCEOOO 16-a-HYDROXYOESTRADIOL see EDU500 3-HYDROXY-OESTRA-l,3,5(10)-TRIEN-17-ONEsee EDVOOO... 

Five-membered heterocycles have been used as substitutes for the y-lactone ring of cardenolides. Thus, the 17 -(5 -isoxazolyl)- and 17)8-(3 -pyrazolyl)-cardenolides (526) and (527) have been prepared from 20-ethoxy-21-formyl-3 -acetoxy-17)8-pregna-5,14,20-triene (528) by reaction with hydroxylamine and hydrazine hydrate, respectively. The isomeric 14a,15a- and 14) ,15/S-epoxides (529) and (530) in both series were then obtained by peracid treatment or alkaline cyclization of the respective 14,15-bromohydrin. 

The extremely labile triene-enol-lactone 16.1 was found to be involved in the rapid yellowing of the milky juice and flesh of L. chrysorrheus and L. scrobiculatus, and it could be isolated from the mushrooms under special mild conditions (46). The strong UV absorption of compound 16.1 at... 

Figure 5.1a (Continued) octadiene-3,6-diol) (11) hydroxycitronellol (3,7-di methyloctane-l,7-diol) (12) 8-hydroxydihydrolinalool (2,6-dimethyl-7-octene-l,6-diol) (13) 7-hydroxygeraniol (E-3,6-dimethyl-2-octene-l,7-diol) (14) 7-hydro-xynerol (Z-3,6-dimethyl-2-octene-l, 7-diol) (15) cis and trans 8-hydroxy linalool (E- and Z-2,6-dimethyl-2,7-octadiene-l,6-diol) (16) p-menthenediol I (p-menth-l-ene-7,8-diol) (17) E-geranic acid (3,7-dimethyl-2,6-octadienoic acid) (18) E-2,6-dimethyl-6-hydroxyocta-2,7-dienoic acid (19) E- and Z-sobrerol or p-menthenediol II (p-menth-l-ene-6,8-diol) (20) cis and trans rose oxide (21) nerol oxide (22) 2-exo-hydroxy-1,8-cineol (23) 1,8-cineol (24) wine lactone (25) cis and trans 1,8-terpin (26) triol (2,6-dimethyloctane-2,3,6-triol) (27) hotrienol [(5E)-3,5-dimethylocta-l,5,7-trien-3-ol] (28) myrcenol (2-methyl-6-methylene-7-octen-2-ol)...

The Chemistry of Rii% b.— The 9— 6p lactone (44, R = H) of the 12-methoxy-podocarpa-8,ll,13-triene series was obtained by the successive dehydration of the 7a- and 7)3-hydroxy-lactones with toluene-p-sulphonic acid in acetic anhydride and hydrogenation of the resulting A -enol-lactone over palladium-charcoal. Examination of the width of the C-6 proton resonance led to the... 

Intramolecular functionalisation of the isopropyl group of dehydroabietic acid has been achieved by the cyclisation of 12-carboxy-group to form a y-lactone (73) using lead tetra-acetate as the oxidant. Thermolysis of the 12-diazomethyl ketone also leads to cyclisation. Direct replacement of the isopropyl group by a nitro-group occurs in the nitration of methyl 12-acetylabieta-8,l 1,13-trien-18-oate. The 13-nitro-compound (74) was converted through the amine to... 

Ascidiatrienolide A (85) and neodidemnilactone (88) proved to be geometrical isomers of the triene moiety with the same absolute configurations of the stereocenters on the lactone ring part. 

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