Lactone-directed

The hydrogenation of 63 occurred quantitatively and with high stereoselectivity (25 1 in favour of 62). The regioselectivity was similarly good in the Baeyer-Villiger rearrangement (12 1) in favour of 61 over the isomeric lactone. Attempts to convert the lactone directly to 60 X = z-Bu gave only low yields. 

Thus cyclopentene reacts with tribromomethyl phenyl sulfone to give a high yield of addition product (equation 106). Samarium iodide catalysis gives a good yield of addition product upon reaction of l-chloro-2-iodoethanes with 1-alkenes (equation 107)690. The product from this reaction has been used to prepare a cyclic target molecule in several further steps. a-Bromoesters also undergo a similar reaction, the product from which upon treatment with KOH gives lactones directly. 

Many of the methods listed for the preparation of hydroxy acids (Table 47) have been used to prepare lactones directly. Reduction of levulinic acid, CHjCOCHjCHjCOjH, by sodium and alcohol or by catalytic hydrogenation over Raney nickel leads to "y-valerolactone. S-Captolactone is prepared in a similar manner from y-acetobutytic acid. Other S-lactones have been formed by catalytic hydrogenation of the corresponding aldehydo... 

The oxidation of L-rhamnose was carried out by Will and Peters and by Rayman. These workers isolated the lactone directly from the bromide-free solution without the intermediate salt stage. The product crystallized readily. This is one of the few instances where such a procedure can be carried out. As the calcium and barium salts were... 

Ketones of the form RCOCH3 and RCOCH2R can be carboxylated indirectly by treatment with magnesium methyl carbonate 56. " Because formation of the chelate 57 provides the driving force of the reaction, carboxylation cannot be achieved at a disubstituted a position. The reaction has also been performed on CH3NO2 and compounds of the form RCH2N02 " and on certain lactones. Direct carboxylation has been reported in a number of instances. Ketones have... 

The lactone-directed intramolecular Diels-Alder cycloaddition was the key step in D.F. Taber s synthesis of trans-dihydroconfertifolin. During the endgame, the Simmons-Smith cyclopropanation was utiiized to install the gem-dimethyl group at C4. The trisubstituted alkene was cyclopropanated in excellent yield and the resulting cyclopropane was subjected to catalytic hydrogenation. 

Taber, D. F., Nakajima, K., Xu, M., Rheingold, A. L. Lactone-Directed Intramolecular Diels-Alder Cyclization Synthesis of trans-Dihydroconfertifolin. J. Org. Chem. 2002, 67, 4501 504. 

Lactonization. Corey et al. have reported further studies on this method for lactonization directed mainly toward elucidation of the mechanism. One useful observation is that lactones containing from 12 to 21 members are formed at about the same rate, but at a rate much lower than that for formation of 5- or 6-membered lactones. ... 

Racemic Malolactonate. The first cyclic monomer prepared was the benzyl ester of the 3-lactone of malic acid. Initial attempts to make the lactone directly from malic acid itself were unsuccessful, so bromosuccinic acid was chosen as the starting material. This compound was converted to its anhydride by refluxing in acetyl chloride, and the anhydride was reacted with benzyl alcohol to yield a mixture of the two bromosuccinic acid monobenzyl ester isomers. Only one of these esters, IIIB, is capable of being converted to the lactone by... 

It is interesting that the ring forms of the sugars, rather than the free aldehyde, are oxidized directly under these conditions 189). Pyranoses yield 6-lactones and furanoses 7-lactones, directly. 

Taber DF, Nakajima K, Xu M et al (2002) Lactone-directed intramolecular Diels-Alder cyclization synthesis of trans-dihydroconfertifolin. J Org Chem 67 4501-4504... 

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