Lactones 315, Table

Carbonylation of alkyl halides to yield esters and lactones (Table 8.5)... 

Carbonylation of alkynes to give 2-substituted 4-methyl-y-butyro-lactones (Table 8.9)... 

As discussed in Sect. 3.4, the synthon 20 was prepared from the dibromo-heptonolactone, which in turn was obtained from the cheap commercially available D-g(ycero-D-gM/o-heptono-l,4-lactone (Table 1). The other isomeric dibro-moheptonolactones shown in Table 1, which were prepared from the heptonates, obtained from chain extension of o-mannose and o-galactose, respectively, were also converted into unsaturated bromodeoxyheptonolactones. Finally, we obtained 2-0-acetyl-7-bromo-3,7-dideoxy-D-x7(o-hept-2-enono-l,4-lactone and the corresponding D-/yxo-isomer by the Kiliani extension of o-gulose. These substrates were all cyclized to cyclopentane lactones, stereoisomers of 65 [98]. 

The ring size has a determining effect on the threshold values not only in the case of the sweet-bitter 1-amino-cycloalkane-1-carboxylic acids but also, as our investigations have shown, in the case of other cyclic compounds, as for example the bitter cyc-loalkanones, azacycloalkanes, lactams and lactones (Table XV), as well as the sweet cycloalkanesulfamates (Table XVI). From the tables it follows that the hydrophobic contact with the receptor apparently attains a maximum in general with ring sizes 6-8 on the part of sweet as well as bitter compounds. 

The indium-mediated Reformatsky reaction of phenyl a-bromoalkanoates with ketones or aldehydes gives di-, tri-, and tetrasubstituted /3-lactones (Table 21).327-329 A similar reaction of imines with ethyl bromoacetate gives 3-unsubstituted /3-lactams (Equation (83)).330 331... 

An enzyme isolated from F. oxysporum catalyzes the hydrolysis of various aldonate and aromatic lactones (Table 19.1) (Shimizu et al, 1992). The hydrolysis of aldonate lactones proceeds stereospecifically through recognition of... 

Simple mono- or di-substituted enol ethers may be oxidized to esters and lactones (Table 8, entries 1 and 2). However, fully substituted enol ethers undergo oxidative cleavage, since the proposed mechanism for oxidation to an ester involves a hydride shift which can no longer take place. 

Dihydropyrans need only a moderate excess of PCC to be converted into unsaturated lactones (Table 8, entry 6)." However, the oxidation of normal allylic and benzylic C— H groups requires a large excess of PCC (Table 8, entries 7 to 9). " The amount of PCC needed is lower if benzene" " or DMSO are used as solvents for oxidation, but the reactions still need to be heated to obtain reasonable conversion. 

The direct fluorination with elemental fluorine at — 78 "C of trimethylsilyl enol ethers derived from diketones results in the formation of the corresponding monofluoro diketones 11 in moderate yield. The trimethylsilyl ethers from cyclic diketones undergo smooth fluorination to give the enol forms, c.g. 12, and not the keto forms.Higher yields are generally observed for the analogous reactions of silyl derivatives of esters, carboxylic acids, malonates, dimethyl amides and lactones (Table 4). ... 

Selenolactonization of ( )-m-6-methyl-2,4-cycloheptadienylacetic acid gave a mixture of 1,2-anti- and l,4-.t>>n-addition products which could be separated. Each product rearranged in a highly suprafacial manner to the substituted hydroxycycloheptenvl lactones (Table 8, entries 6... 

Nevertheless, it was necessary to give three equations with different constants for penicillins with an a-amino or a-ether group in the side-chain, or with an ortho aromatic ether group (methicillin analogues). It was suggested that the mechanism involves hydrophobic binding and /3-lactam antibiotics are able to bind to serum when ionic sites for this are not available, e.g. the case of penicillin amides, cephalosporin lactones (Table 8.9) and certain 2-substituted cephalosporins (Table 8.7), when the increased lipophilicity leads to increased serum binding. 

Workers have used NMR spectroscopy to assign structures to the 5- and 6-sulfate esters of L-ascorbic acid and to the 4Z and 4E isomers of 2-sulfo-2,3,4,6-tetrahydroxyhexa-2,4-dienoate-8-lactone (Table V). Sulfonation at C6 (C5) of L-ascorbic acid shifted the signal of C6 (C5) downfield by 7-8 ppm the signal(s) of the adjacent carbon(s) moved slightly upheld (18). Those shifts were noted previously by others (19) in sugar sulfates. When I was dissolved in concentrated sulfuric acid-d2, NMR shows approximately 90% monosulfonation at C6 (18). 

Alkylation of the lactone (Table 4, entries 5 and 6) which is optically enriched (33 % ee) gives only racemic product53, indicating that a truly symmetrical weso-Jt-allyl complex and not a cr-Pd—C species is involved. 

Similar to the reduction of 3-oxo acids, 4- and 5-oxo acids and Iheir corresponding esters are reduced by baker s yeast to the (/ -configurated alcohols, often in high enantiomeric excess. In general, the reduced products are isolated as the corresponding y- and d-lactones (Table 6) which have an alkyl substituent of 2 to 13 carbon atoms in length171,172,174. 

Lactones (Table 19) were slowly reduced to di-alcohols. The rate limiting step in this reaction was probably the hydrolysis of the lactone ring, which was slow at pH 5.5. 2-Hydroxypyridine-5-carboxylate was converted to 3-hydroxymethylpyridine. That means the 2-hydroxy group was reductively eliminated. Racemates of chiral substrates carrying a chiral carbon atom in a-position were reduced, too, but in no case could marked stereospecificity be found. Reactions with (K,5)-2-(4-chlorophenoxy)-propanoate were stopped after 50 % reduction. Both enantiomers of the 2-(4-chlorophenoxy)-propan-l-ol... 

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