7-Butyrolactones, 2,4-disubstituted synthesis

The reaction shown in Eq. 9.47 demonstrates a short synthesis ofy-[(trityloxy)methyl]-a-alkylidene-y-butyrolactones having stereodefmed mono- and disubstituted exo-alkylidene... 

Intriguingly, the enantiomeric trans-disubstituted y-butyrolactone (-)-75, completing a formal synthesis of (-)-methylenolactocin (11) [47], can be obtained by cyclizing 67 through an iodolactonization after protection of the free OH group (Scheme 11). 

The cyclopropane aldehyde 156 was identified as a versatile chiral building block for the enantioselective synthesis of 4,5 disubstituted y-butyrolactones of type 158 or 159. Both enantiomers of 156 can be easily obtained in a highly diastereo- and enantioselective manner from fixran-2-carboxylic ester 154 using an asymmetric copper-catalyzed cyclopropanation as the key step followed by an ozonolysis of the remaining double bond (Scheme 25) [63]. Addition of... 

Tamaru Y, Mizutani M, Furukawa Y, Kawamura S, Yoshida Z, Yanagi K, Minobe M (1984) 1, 3-asymmetric induction highly stereoselective synthesis of 2,4-trans-disubstituted y-butyrolactones and y-butyrothiolactones. J Am Chem Soc 106 1079-1085... 

The sequential dialkylation of S-y-trityloxymethyl-y-butyrolactone (92) and subsequent lactone carbonyl transposition provides a highly stereoselective synthesis of /3,/3-disubstituted-y-butyrolactones (93) (Scheme 64). This process is complimented by the report that the lactone (92) may be converted into its / -enantiomer using the Mitsunobu inversion procedure. ... 

Lactonization of a hydroxy-acid to a butyrolactone is achieved, using dimethyl-formamide dineopentyl acetal, during a synthesis of oxygenated nor-heliango-lides. The chiral lactone (164) is prepared from (iJ)-malic acid, its dianion is alkylated at carbon to give the /ra/i5-disubstituted lactone (165) in moderate yield, and this is used in a synthesis of (—)-aplysistatin (Scheme 94). An independent, biogenetically patterned synthesis of this natural product, using tetronic acid intermediates, has been described. ... 

Addition of tributylstannyl-lithium to crotonaldehyde and protection of the resulting alcohol with chloromethyl methyl ether gives the stannane (192), which reacts with both alkyl and aryl aldehydes RCHO to form specifically the t/rr o-hydroxy-enol ethers (193). These latter compounds have been used to prepare tra/i5-4,5-disubstituted butyrolactones by hydrolysis and subsequent oxidation. Palladium-catalysed carbonylation of RX in the presence of organotin species constitutes a useful synthesis of unsymmetrical ketones, and in the example reported this year RX is an arenediazonium salt. The reaction, which is basically an aromatic acylation, proceeds in good to excellent yield. Another Pd-catalysed reaction of aromatics, this time aryl bromides, is their reaction with acetonyltributyltin (194), prepared from methoxytributyltin and isopropenyl acetate, to give the arylacetones (195). ... 

P.V. Ramachandran, D. Pratihar, D. Biswas, Control of stereochemistry a general synthesis of cis- or frans-p,Y-Disubstituted-y-butyrolactones... 

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