Bicydic lactones

The effect of solvent and sensitizer on the course of photolysis of pyran-2-one is evident from Scheme 11. When methanol is present, either the ring is cleaved and an ester (237) is formed, or, with a sensitizer, dimers (238) are produced in equal amounts. The bicydic lactone (227) and the ester (237) are believed to be formed via singlet excited states of the pyranone while the dimers (which are photostable) result from the triplet state (68TL5279). 

A by now classic retrosynthesis of prostaglandins PGFj and PGEj (Fig, 4) leads to the bicydic lactone [12), five-carbon phosphonium salt [13], and phosphonate [14] (19). These compounds contain all the carbon atoms of the prostaglandins and, in [12], aU but one of the chiral centers. Lactone [12] has come to be knovm genetically as the Corey lactone, and its synthesis in one enantiomeric form has been the subject of numerous complementary investigations. 

Menendez and coworkers [75] developed a domino reaction of a-nitrocycloalkanones 128 with a-alkyl a,P-unsaturated aldehydes 129 in water, which led to functionalized bridged bicydic lactones 130 containing 10-, 11-, 13-, and 15-membered rings with complete stereocontrol depending on the ring size (Scheme 12.51). The structures of the products were determined by X-ray diffraction analysis. 

Furthermore, ketene dithioacetals 83 prepared from unsaturated ketones 82 by means of Peterson reactions are converted to the bicydic lactones 84 by treatment with cerium(IV) ammonium nitrate (CAN) in wet acetonitrile (Scheme 2.51) [142]. The oxidative cydization occurs stereosdectively in moderate yields. 

Patil, A.D., Freyer, A.J., Bean, M.F., Carte, B., Wesfley J.W., Johnson, R.K, and Lahouratate, P. (1996c) The plakortones, novel bicydic lactones from the sponge Plakortis halichondrioides activators of cardiac SR-Ca pumping ATP-ase. Tetrahedron, 52, 377-394. 

Fragmentation of 1,3-diols 7-34 Decarbonylation of p-hydroxy carboxylic acids and of p-lactones 7-36 Elimination of CO and C02 from bridged bicydic compounds 7-43 Pyrolysis of P-hydroxy olefins 7-44 Pyrolysis of allylic ethers... 

Several of the seminal routes to the lactone, as devised by Corey, are summarized in Fig. 5. Diels-Alder reaction of (methoxymethyl)cyclo-pentadiene [15] with chloroacrylonitiile and then basic hydrolysis gave the bicydic ketone [16] (20). Ring expansion in a selective Baeyer-Villiger reaction led to lactone [17] that was then hydrolyzed to hydroxy add [18],... 

A further series of prochiral bicydic [2.2.1] substrates have also been studied by Taschner and coworkers and lead generally to lactones of high enantiomeric purity. One of these is a valuable precursor for chorismic acid synthesis[97]. 

Also with starting compounds containing two oxygen nucleophiles, both alkoxy/ amino carbonylation and cyclocarbonylation (carbonylative cydization to lactone) mechanisms can occur in sequence. Some bicydic y-lactones from parasitic wasps (Hymenoptera Braconidae) were synthesized by hydrolytic kinetic resolution of epoxides and palladium(II)-catalyzed hydroxycyclization-carbonylation-lactoniza-tion of enediols. For example, cis- and trans-5-n-hexyl-tetrahydrofuro[3,2-b]furan-2 (3H)-ones 75 and 76, with the (3aR,5R,6aR) and (3aS,5R,6aS) configurations, respectively, were acquired in six steps from the inexpensive, readily available ridnoleic add 74 (Scheme 13.48) (89). 

Paddon-Jones, G.C., McErlean, C.S.P., Hayes, P., Moore, C.J., Konig, W.A. and Kitching, W. (2001) Synthesis and stereochemistry of some bicydic y-lactones from parasitic wasps (Hymenoptera Braconidae). Utility of hydrolytic kinetic resolution of epoxides and palladium(II)-catalyzed hydroxycyclization[Pg.360]

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