Lactone unit

Five-membered lactones (y-butyrolactones) fused to carbohydrates have proven to be convenient synthons towards branched-chain sugars through opening of the lactone unit. Velaskes et al. [208] described the synthesis of y-butyrolactones... 

Resonance within the unsaturated lactone unit of coumarin gives a strong hint as to its likely reactivity. Thus, the oxygen atom of the carbonyl group receives electron density both via the enone chromophore and from the internal resonance of the lactone group (Scheme 5.2). 

Myriad natural products such as carbohydrates, ionophore antibiotics and many others possess polysubstituted oxygenated rings, such as furans, pyrans and lactone units, within their complex structure. Pyran and dihydropyran units are par-... 

Fig. 4. Bryostatin 3 is special because of the y-lactone unit at the C-ring.

A similar convergent synthetic strategy was applied in our synthesis of annona-cin, using sequential assembly of the three key fragments, aldehyde 29, phospho-nium 30, and alkyne 14 (Scheme 10-9). In this synthesis, the a,p-unsaturated-y-lactone unit was constructed after completion of the linear skeleton. A modified method was applied into the synthesis of segment 3 (Scheme 10-5), in which the six carbons, as well as two chiral centers from D-glucono-8-lactone, were all incorporated into the final target. Therefore, the efficiency of the whole... 

The IR spectrum of kopsilactone indicated the presence of a y-lactone unit (1770 cm ) which was supported by the observation of a quaternary carbon resonance at S 176. The observed J) value of 11 Hz required a rrans-diaxial arrangement between H(3a) and H(4P), while the estimated value of ca. 4 Hz suggested a ds-relationship between H(4) and H(S). An equatorial H(5) requires a cis ring junction between the piperidine and the five-membered ring which in turn fixes the stereochemistry of the lactone-piperidine ring junction. 

Using enantiomerically pure 4-hydroxy-2-alkynoate and 1,11-dodecadiene with CpRu(cod)Cl as catalyst, this reaction type was used in the synthesis of the acetogenin (+)-ancepsenolide, a bisbutenolide with a 12-carbon chain linking both lactone units "4. The primary addition step of this conversion represents an example of a ruthenium-catalyzed Alder-ene reaction (vide infra). Other examples of this type have been reported123. 

Bridged /rauj-decalin-2-yl radicals are formed in cyclization reactions of bicyclic iodolac-tones55. The stereoselectivity in hydrogen-abstraction reactions is very similar to reactions of unbridged, monocyclic radicals with equivalent a- and /Fsubstituents. The bridging lactone unit, therefore, seems to have little influence on the sleric course of the reaction, and preferential attack from the axial side occurs. Axial substituents in / -position to the radical center further increase the selectivity and only the product arising from axial attack is found. 

Ij-PhI(OAc)2 is valuable in performing a skeletal simplification of a bridged ketone, which is necessary for a synthesis of (+)-cw-lauthisan. Actually, the degradation of the y-lactone unit also enlists the same combination of reagents. ... 

Fig. 6 Structures of cyclic allyl methacrylate free radicals [73]. (a) <5-lactone unit with carbonyl stretch frequency at 1740 cm and 1230 cm (b) y-lactone unit with carbonyl stretch frequency at 1775cm and 1275cm . ...

In the presence of a Lewis acid, silyl enol ethers can be alkylated with reactive secondary halides, such as substituted benzyl halides, and with chloromethylphenyl sulfide (ClCH2SPh), an activated primary halide. Thus, reaction of the benzyl chloride 10 in the presence of zinc bromide with the trimethylsilyl enol ether derived from mesityl oxide allowed a short and efficient route to the sesquiterpene ( )-ar-turmerone (1.22). Reaction of ClCH2SPh with the trimethylsilyl enol ethers of lactones in the presence of zinc bromide, followed by 5-oxidation and pyrolytic ehmination of the resulting sulfoxide (see Section 2.2), provides a good route to the a-methylene lactone unit common in many cytotoxic sesquiterpenes (1.23). Desulfurization with Raney nickel, instead of oxidation and elimination, affords the a-methyl (or a-alkyl starting with RCH(Cl)SPh) derivatives. ... 

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