Simple methods to find the stereochemistry of the side chain of .gamma.-lactones

Narayanan, C. R.; Venkatasubramanian, N.

doi:10.1021/jo01272a028

Cited by 55 publications

(14 citation statements)

References 2 publications

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“…* Similarly, if a-santonin were to be hydrolysed to (11) we must assume that dehydration to (12) is slower than relactonisation: for if (12) were to be formed during the reaction there would be deuterium incorporation at C-7 of the desmotroposantonin ultimately produced. Similar arguments exclude the formation of (13). It does, however, seem possible that the hydroxy acid (1 1) could rearrange, by a dienone-phenol reaction, followed by rapid conversion into a-desmotroposantonin as discussed later.…”

Section: Mementioning

confidence: 78%

“…Ring B is quite flexible and is believed to exist in a chair-like form with the 6-oxygen pseudo-axially attached, although a boatform is readily adopted. 13 The cation formed by methyl migration from C-10 to C-1 can be stabilised by overlap of the x-system with either the lone pair electrons from 0-17 of the lactone ring or from 0-17 and the 18-oxygen atoms of a hydrated lactone. To maximise these stabilising interactions, the lactone ring can fold quite close to ring A, with ring B in a boat conformation.…”

Section: Mementioning

confidence: 99%

See 1 more Smart Citation

Kinetics and mechanism of the acid-induced rearrangements of α-santonin, 6-epi-α-santonin, and related compounds

Waring¹

1984

J. Chem. Soc., Perkin Trans. 2

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Section: Mementioning

confidence: 78%

Section: Mementioning

confidence: 99%

Kinetics and mechanism of the acid-induced rearrangements of α-santonin, 6-epi-α-santonin, and related compounds

Waring¹

1984

J. Chem. Soc., Perkin Trans. 2

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“…155-156", identical (i.r., mixed m.p., and t.1.c.) with the sample obtained from dihydro-P-cyclopyrethrosin (3), while fraction I1 yielded 14 mg of desacetyldihydro-P-cycloisopyrethrosin (7).…”

Section: Hydrolysis Of Chrysaninmentioning

confidence: 99%

Sesquiterpene Lactones from Pyrethrum Flowers

Doskotch¹,

El‐Feraly²,

Hufford³

1971

Can. J. Chem.

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Three new sesquiterpene lactones, dihydro-P-cyclopyrethrosin (3), chrysanin (4), and chrysanolide (5) were isolated from the flowers of Chrysanthemum cinerariaefolium and their structures determined by physical and chemical methods. The configuration at C-1 of pyrethrosin (2) was established as R by its conversion to dihydro-P-cyclopyrethrosin (3), a hydrogenation product of P-cyclopyrethrosin (I), which had the C-1 hydroxyl group assigned by the Horeau procedure and Brewster's benzoate method. The preparation and properties of the C-11 epimers, 12 and 17, of dihydropyrethrosin are reported and their stereochemistry established.L'extraction des fleurs du Chrysanthemum cinerariaefolium permet d'isoler trois nouvelles lactones sesquiterpeniques: la dihydro 0-cyclopyrkthrosine (3) la chrysanine (4), et la chrysanolide (5); leur structure a pu Ctre dkduite grbce a des m6thodes physiques et chimiques. Grlce une corrklation avec la dihydro 8-cyclopyrkthrosine (3), un produit d'hydrogknation de la 0-cyclopyrethrosine (1) pour laquelle la configuration de I'hydroxyle en position 1 a pu Ctre attribuke par les m6thodes de Horeau et de Brewster, on a pu ktablir que la configuration en C-1 de la pyrkthrosine (2) est R. On rapporte aussi la I prdparation, les propridt6s et la fagon de dkterminer la stkrdochimie des Bpimbres 12 et 17 en C-11. In a previous publication (I), we reported the isolation of P-cyclopyrethrosin (1) from the flowers of Chrysanthemum cinerariaefolium Visiani. Prior to this, pyrethrosin (2), the first recognized germacranolide was the only sesquiterpene lactone obtained from this source (2). By careful chromatography of a fraction of the pyrethrum flower extract, three additional sesquiterpene lactones, dihydro-P-cyclopyrethrosin (3), chrysanin (4), and chrysanolide (5) were isolated.The isolated dihydro-P-cyclopyrethrosin (3) was identical (m.p., i.r., n.m.r., and specific rotation) with the hydrogenation product of P-cyclopyrethrosin (1). The stereochemistry at C-1 1 was determined from the value of the n.m.r. coupling constant between H-7 and -11, and the application of the relationship of Narayanan and Venkatasubramanian (3). The C-1 1 proton in the 100 MHz spectrum appears as six peaks at 6 2.64, the X of an A,MX pattern, where JH7-H,, = 12.0 and JH,,-H,, = 6.8 Hz. The C-11 proton is, therefore, pseudo-axial as shown in the Newman projection6. The preparation of desacetyldihydro-P-cycloisopyrethrosin (7), a hydrolysis product of dihydro-P-cyclopyrethrosin (3), in which the lactone is to C-6 confirmed the assignment. The C-11 proton becomes pseudo-equatorial as in 8 and the pattern1 changes to five peaks located at 6 2.80, JH7_,,, = 7.7 HZ.The assignment of stereochemistry at C-1 in P-cyclopyrethrosin (1) and its dihydro-derivative 3 has yet to receive unambiguous experimental support. Iriuchijima and Tamura (2d) in their study of the u-and P-dihydrocyclopyrethrosin mixture, derived from pyrethrosin by cyclization, utilized the coupling constant values ( J = 5 and 10.5 Hz) for the H-1 pattern to ass...

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“…The stereochemistry of the C-11-methyl group was assigned on the basis of chemical shift dierence studies and coupling constant. 4 Reduction of compound 2 7 with this reagent combination furnished only one major product 8 in 90% yield.…”

mentioning

confidence: 93%

Selective Reduction of the Exomethylene Group of α-Methylene γ- or δ-Lactones with CdCl2–Mg–MeOH–H2O‡

Bhattacharya¹,

Jain²,

Sharma³

1998

J. Chem. Res.

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Simple methods to find the stereochemistry of the side chain of .gamma.-lactones

Cited by 55 publications

References 2 publications

Kinetics and mechanism of the acid-induced rearrangements of α-santonin, 6-epi-α-santonin, and related compounds

Kinetics and mechanism of the acid-induced rearrangements of α-santonin, 6-epi-α-santonin, and related compounds

Sesquiterpene Lactones from Pyrethrum Flowers

Selective Reduction of the Exomethylene Group of α-Methylene γ- or δ-Lactones with CdCl2–Mg–MeOH–H2O‡

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