Isophotosantonic lactone

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-... 

Show that the stereochemistry of lumisantonin and isophotosantonic lactone formed from a-santonin are consistent with the mechanisms presented in this chapter. 

In acidic solution the rearrangement of a-santonin to lumisantonin and then ultimately to photosantonic acid is not as efficient as rearrangement to the hydroxy ketone, isophotosantonic lactone (5), shown on page 308. Fisch and Richards(6) found that the photorearrangements of a-santonin could be sensitized with benzophenone or Michler s ketone. Moreover, if the irradiation of a-santonin (3660 A) is carried out in piperylene as solvent, the photoreaction is completely quenched. This suggests that the rearrangements proceed via triplet states. 

There are probably no photochemical transformations which are more intriguing to the organic chemist than the deep-seated skeletal rearrangements of dienones (7-11). An interesting and thoroughly studied example is that of the dienone santonin (III), whose complex transformations are outlined in Chart I. Lumisantonin (8, 9) (IV) results from the irradiation of santonin in dioxane. Isophotosantonic lactone (8) (V) is formed on photolysis of santonin instead in aqueous acetic... 

The same mechanistic reasoning applied to the 4,4-diphenylcyclo-hexadienone case proves applicable to the photochemistry of santonin, as outlined earlier furthermore, this mechanism leads to the correct stereochemistry of lumisantonin (IV) and of isophotosantonic lactone (V) as derived experimentally (11-13). Chart III delineates the application to the formation of lumisantonin (IV). 

The thermal conversion of lumisantonin to isophotosantonic lactone poses no special problems. 

That solvent incorporation becomes a dominating feature of dienone photochemistry in protic media was again recognized for the first time with santonin (28) which was converted to isophotosantonic lactone (31) in aqueous acetic acid (Chart 4). In addition to 5/7-fused hydroxy-ketones, spirocyclic isomers may be formed as well irradiation of 1-dehydrotestosterone acetate (32a) in aqueous acetic acid gave approxi-... 

Irradiation of santonin with UV light in AcOH solution results in the formation of isophotosantonic lactone (171) in a well documented process... 

The reaction was tested with several santonin and isophotosantonic lactone derivatives (1, 5, 105, and 171) that, after treatment with diazomethane, gave the corresponding methyl esters 446-448. The reaction behavior was not especially dependent on the stereochemistry of the lactone since 6-e/7i-santonin (105) was reduced in almost identical yield, nor was it dependent on the nature of the enone since the reaction also proceeded with dienone 1, enone 5, and cyclopentenone 171. In the latter case, PhSeNa was found to be better than PhSNa. 

Formylbutyl)-2-methoxy-3-methylbenzoic acid, methyl ester, Y11.4 Isophotosantonic lactone, T22.14... 

A early partial synthesis of the guaianolide nucleus was based on photochemical rearrangement of a-santonin (44) to give isophotosantonic lactone (45) [17] (Scheme 98.5). The stereochemistry of this reaction is remarkable. Irradiation of the santonin isomer, in which the C6-06 bond is 3 disposed gives the C6-06, C7-C11 cis isomer of 45 [18]. 

Scheme 983 Photochemical Fcarrangement of a-santaim (44) into isophotosantonic lactone (45)...

Isophotosantonic lactone, T22 Isophyllocladene, T36 Kynurenine, A20 Longiborneol, T28 Longicyclene, T28... 

Upon photolysis in nucleophilic media, like water or ethanol, mazdazantonin gives the ring cleaved acid or ester derivative while a-santonin when photolysed in water gives isophotosantonic Lactone. 

Isoneomatabiol, T14 Isonepetalactone, T14 Isonootkatone, T23 Isooleanonic acid, dimethyl ether, T42 Isopapuanic acid, Y12 Isopatchoulane, T27 Isopavine alkaloids, K1 Isopelletierine, K19 Isopeulustrin, Yl Isophorbol triacetate, T39 Isophotoartemisin acetate, T21 Isophotosantonic lactone, T22 Isophyllocladene, T36... 

Formylbutyl)-2-methoxy-3-methylbenzoic acid, methyl ester, Y11.4 Isophotosantonic lactone, T22.14 Vulgarin, T22.3 Illudin S, T30.9 Laccijalaric acid, T29.3 Hirsutic add, T31.12 Pulchellin C, T 9.1 Ambrosic acid, T 93 Plenolin, T 9.6 Florenilanin, T 9.10 Abscisic acid, T 17.8... 

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