Co-methylated lactones

Fig. 11 Enantioselectivity in the CALB-catalyzed transesterification of co-methyl lactones [75]...

Extension of DKR to polymer chemistry would readily result in chiral polyesters, polycarbonates, or polyamides from an optically inactive monomer mixture. Scheme 10 describes three variants of chemoenzymatic catalysis applied in polymer chemistry that recently appeared in the literature. Route A uses AA and BB monomers to prepare chiral polymers from racemic/diasteromeric diols. Route B converts an enantiomer mixture of AB monomers to homochiral polymers. Route C is the enzymatic ring-opening polymerization of co-methylated lactones to homochiral polyesters. Details will be given in Sect. 3.4.2. 

Chiral Polymers from Racemic co-Methylated Lactones... 

Scheme 12 Chiral polymers from racemic co-methylated lactones by iterative tandem catalysis [105, 106]...

Fig. 10 EnantiopreferenceofCALB-catalyzed (a) hydrolysis of methyl-substituted 8-caprolactones [82], (b) hydrolysis of 4-alkyl-substituted 8-caprolactones [83], (c) transesteiification of 6-alkyl-substituted 8-caprolactones [84], and (d) transesteiification of co-methyl-substituted lactones [85]...

Novozym 435-catalyzed ROP of co-methylated six lactones (4-, 6-, 8-, 9- and 13-membered ring) was studied for elucidation of the relationships between enantioselectivity and lactone structure [147]. The rate of polymerization was much affected by the ring size as suggested by fccat values, and the enantioselectivity was switched from (5)-selective for small (4-, 6-, and 7-membered) lactones to (7 )-selective for large (8-, 9-, and 13-membered) lactones. The selectivity switch... 

The effect of lactone ring-size on the inhibition was studied, for N-acetyl-)3-D-glucosaminidase from bovine epididymis, with lactones and lactone derivatives unable to undeigo ring-isomerization, by Pokomy and co-workers. From a comparison of Kj values for 2-acetamido-2-deoxy-D-glu-cono-1,5-lactone (0.45 nM) with the 1,4-lactone (4.5 fiM) and of Kj for the methyl ) -furanoside with that for the pyranose (4 mM), it was concluded that the 1,4-lactone has an 10-fold lower inhibitory potency than the 1,5-lactone. The weak inhibition by the 5,6-O-isopropylidene derivative of the... 

In aqueous acid cross-conjugated cyclohexadienones are principally photoconverted to one or more hydroxy ketones. In the case of a-santonin (1), isophotosantonic lactone (5) is formed in about 50% yield. A series of papers by Kropp and co-workers has aided in understanding this reaction/32-39-411 They have shown that the presence of a 4-methyl group (steroid numbering) results in the preferential formation of the 5-7 fused ring system (isophoto-... 

Gassman and co-workers have recently investigated the photoinduced cy-clization of y,5-unsaturated carboxylic acids to y-lactones [100]. 5-Methyl-4-hexenoic acid 51 is converted into the radical cation 52. The cyclization of 52 is expected to yield the distonic radical cations 53 and 54, which leads to the anti-Markonikow products 55 and 56 in ratio 5 1. Fine-tuning of the sensitizer improved combined yields up to 89% [101],... 

Renaud and co-workers used 78 for the synthesis of (-)-phaseolinic acid (6) and (-)-pertusarinic acid (8) (Scheme 12) [32, 33]. Radical addition of dimethyl phenylselenomalonate to 78 proceeded with rearrangement of the bicyclics to yield the seleno-acetal 79 [34]. After reductive deselenylation and Baeyer-Villiger oxidation treatment of 80 with BU4NI and BBr3 led to a simultaneous cleavage of the ether, the lactone, and the methyl ester func-... 

When l,8-diaza[5.4.0]bicycloundec-7-ene (DBU) and N-methylated TBD (MTBD) were used as catalysts instead of TBD, no polymerization was observed, even with catalyst loading of up to 20 mol% [89]. The lack of activity of these amines was accounted for by the absence of any activation of the lactone, and the activation of the alcohol turned out to be not sufficient. However, the polymerization was successfully carried out by the addition of a thiourea as a co-catalyst to activate lactones, as shown in Fig. 23. Again, p-butyrolactone was not reactive enough and was not polymerized [89]. 

Condensation of propiolic esters with alkenes.2 Methyl propiolate or tetrolate, when activated by complcxation with the C5H5Fe(CO)2 cation (Fp+), condense with alkenes to form cyclobutenes, 1,3-dienes, and lactones. The type of products formed depend on the structure of the alkene. 1,2-Disubstituted alkenes yield cyclobutenes and 1,3-dienes mainly, whereas 1,1-disubstiluted or trisubstituted alkenes form mainly lactones. 

Other polyhalogenated compounds can be used with similar success. CpFe(CO)2 dimer leads to the formation of mixtures of lactones and esters when reacted with an alkene and methyl trichloroacetate [79] with the lactone being the major product (Scheme 3.10). Similar results were reported earlier by Freidlina and Velichko [80]. FeCl3 and Fe(CO)5 are both suitable for catalyzing the addition of methyl dibromoace-tate to electron-deficient alkenes such as methyl propenoate. It was observed that the ratio of products (acyclic vs. lactone) could be tuned by varying the reaction conditions. In all cases, the acyclic product is predominantly formed. Only in the presence of a co-catalyst such as N,N-dimethylaniline are small amounts of lactone observed. Noteworthy, elevated temperatures (above 100 °C) are necessary for this transformation. 

The a-vinylidene-y-lactones 80 are prepared from 5-hydroxy-2-alkynyl methyl carbonates 79 under mild conditions in good yields [19]. The reaction proceeds at room temperature under 1 10 atm of CO. Bidentate ligands, particularly DPPP and DPPF, are the best ligands. 

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