Angelica lactone

Unsaturated y-lactones, c.g., a- (23) and / -angelica lactone (24), are well known. Compounds 23 and 24 are both converted by alkaline catalysts into an equilibrium mixture in which 23 predominates, the amount of the hydroxy form (25) present at equilibrium being exceedingly small. True a-hydroxy furans are unknown, and, although the preparation of both a- and / -bydroxyfurans has been reported, these claims have often been refuted (see, e.g., reference 14). 

Bromo-5-methylene-2(5//)-furanone 133 was obtained from the /3-angelica lactone 129 by using mild simple methods that combine bromination and dehy-drobromination or debromination processes accomplished in a convenient order, as illustrated in Scheme 41 (94T12457). 

The reaction between the chiral furanones (/ )-/3-angelica lactone 129 (Z = H) and 5-hydroxymethyl-2(5//)-furanone 143 (Z = OH) with cyclopentadiene was... 

Reaction of PTAD with a-angelica lactone gives the pyrazolotriazole 97 via an acyl ene reaction,152 and reaction with 4,4-diethyl-3,5-dimethyl-4//-pyrazole 2-oxide gives 98 after heating.153 A mesoionic bicyclic system 99 is proposed as a product from the reaction of DEAZD with triethylborane.154... 

The lactone derivative 158 obtained from D-ribono- 1,4-lactone afforded (—)-(i )-angelica lactone (159a) upon treatment with methanolic ammonia solution (6). In a similar way, Font and coworkers (207) synthesized (+)-(S)-... 

Cycloadditions (253) of butenolides with isoprene afforded a 1 1 mixture of Diels-Alder regioisomers. The selectivity is increased by the use of aluminum trichloride as catalyst. Although the butenolides studied did not react with furan, even in the presence of catalysts, they reacted smoothly with cyclopentadiene. For example, reaction of (—)-angelica lactone (159a) with... 

Scheme 1 Hypothetical formation of lactols and a-angelica lactones in Crematogaster ants...

In the latter compounds, the cross-conjugated dienone is replaced by a fu-ran ring conjugated to an E double bond. Biosynthetically, it is not known if these compounds arise from 1,4-dione precursors such as 138 by a Paal-Knorr type cyclization (Scheme 2) or from the a-angelica lactones 134 by reduction of the lactone carbonyl followed by loss of water. 

Levulinic acid, acting in its lactone form (XXXII) undergoes dehydration and two products have been obtained, - and /3-angelica lactones, (XXXVIII) and (XXXIX), respectively. a-Angelica lactone has been found to polymerize to a tacky resin by the catalytic agency of boron trifluoride. 

The endo- and e.vo-Diels - Alder adducts 37a and 38a, which are the products from the reaction of cyclopentadiene and (7 )-angelica lactone 39a, have been alkylated under the usual conditions (LDA, THF, — 78 °C) with iodomethane, ethyl, butyl and benzyl bromide26. The alkylations are all completely diastereoselective as is expected in these tricyclic examples and yields are in the range of 80-95%. Pyrolysis of 37b and 38b at around 250-290°C for 2-6 days led to the butenolides 39b. 

Schmitt und Schuerch (54) haben inden (XXVII), Mcthylcyclo-penten (XXVIII), 4,5-Dihyi-o-2-methylfuran (XXIX), a-Angelica-lacton (XXX) und 1-Cyanocyclopenten (XXXI) polymerisiert. Fiir die... 

Fig. 2 -31. Reactions of sugars in the presence of concentrated mineral acids, (a) Pentoses (R = H) yield furfural and hexoses (R = CH2OH) hydroxymethylfurfural. (b) On further heating hydroxymethylfurfural is fragmented under liberation of formic acid. The rest of the molecule is rearranged to levulinic acid, which is lactonized to form a- and /3-angelica lactones.

Hydroxymethylfurfural is not volatile by steam. It is prepared from hexoses in the presence of an acid catalyst by short heat treatment to avoid further degradation to levulinic acid. After recovery by solvent extraction hydroxymethylfurfural is purified by distillation. Levulinic acid can be prepared in good yield from hexose-based polysaccharides by heating with acids. In this reaction formic acid is liberated and levulinic acid is easily lactonized to form a- and /3-angelica lactones (Fig. 2-31). 

However, a more direct synthesis of this ether is the catalytic hydrogenation of furfural at moderate temperatures. Angelica lactone, which is formed on... 

Surface Activation. Acid Activation. Acid treatment of cellulose and hemicelluloses generally leads to hydrolysis to monosaccharides, which can subsequently dehydrate and condense to form furan-type compounds such as furfural and its 5-hydroxymethyl adduct. Further reactions lead to polymeric materials of dark color as well as to monomers such as levulinic acid, formic acid, and angelica lactones. Various condensation and solvolysis reactions also accompany the acid treatment of lignin 123). The hydrolysis, dehydration, and condensation reactions have been used to explain formation of covalent bonds between surfaces (85), increase in water resistance (85, 124), and weakening of wood (75) in nonconventional plywood or particle board production. However, very little factual information is available on how far, in terms of the consecutive reactions mentioned, and in what direction, in terms of the parallel reactions mentioned, does the surface of lignocellulosic materials actually change... 

Group 13 sets the frame for the complex world of furanones. Important fruity and caramelic representatives are Furaneol (Flavis 13.010, FEMA 3174) and the corresponding methoxy derivative mesifuran (Flavis 13.089, FEMA 3664). In addition the linalool oxides and angelica lactone are in this group. 

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