Photochemistry of α-keto-imines: a novel synthesis of xylopinine

Kessar, S. V.; Gupta, Y. P.; Singh, Paramjit; Gupta, Sushil K.; Nanda, A

doi:10.1039/c39780000885

Cited by 6 publications

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“…A few alkaloids were synthesised in this manner in yields ranging from 20 to 50% (ref. 4). The procedure is also applicable for the synthesis of the corresponding indole alkaloids (ref.…”

Section: Ohomentioning

confidence: 99%

Generation and trapping of α-oxa and oxo o-quinodimethanes for natural product synthesis

Kessar¹

1987

Pure and Applied Chemistry

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-Photolysis of 1-o-toluyl-3,4-dihydroisoquinolines gives protoberberine alkaloids through the intermediacy of x-hydroxy quinodimethanes and spirobenzyl isoquinol ines. Ortho trimethylsilylmethyl benzoyl chlorides on treatment with fluoride ions afford ketene quinodimethanes which can be trapped with reactive dienophiles. The reactivity pattern of these intermediates is considered in terms of the frontier molecular orbital theory. The synthetic utility of some ketene-quinodimethane equivalents is discussed. Some novel aspects of purely chemical interest are also associated with these reactive intermediates e.g., the unique molecular orbital array of ketenequinodimethane can have an intriguing bearing on the reactivity and the regioselectivity in their 41T + 27r cycloadditions. The a-hydroxy quinodimethanes which are readily generated through photoenolisation (ref. 3) can undergo, besides the widely explored cycloaddition, interesting reactions with electrophiles. We have investigated the competition between these two processes in the substrates of the type shown in fig. 2. Here the hydroxyquinodimethane, formed on irradiation, can yield a protoberberine (path A) or a spirobenzylisoquinoline (path B) alkaloid. In the event, photolysis of the x-keto-imines in methanol followed by sodiumborohydride treatment, smoothly gave protoberberines. A few alkaloids were synthesised in this manner in yields ranging from 20 to 50% (ref. 4). The procedure is also applicable for the synthesis of the corresponding indole alkaloids (ref. 5). Thus it seemed that electrocyclic ring closure pathway (A) prevails. However, unexpected results were obtained when synthesis of the alkaloids with an unsymmetrical substitution patternin ring C or D was undertaken. For example, the ethyl keto-imine on irradiation gave a 13-methylprotoberberine instead of the anticipated 8-methyl protoberberine. Similarly, 11,12-alkoxy compounds were obtained while the 9,10-alkoxy alkaloids were expected. The observed transposition of the groups may be explained in terms of the initial formation of a spiroketone (path B) and its rapid subsequent transformation (ref. 6) as shown (Fig. 3). OHO

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“…A few alkaloids were synthesised in this manner in yields ranging from 20 to 50% (ref. 4). The procedure is also applicable for the synthesis of the corresponding indole alkaloids (ref.…”

Section: Ohomentioning

confidence: 99%

Generation and trapping of α-oxa and oxo o-quinodimethanes for natural product synthesis

Kessar¹

1987

Pure and Applied Chemistry

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Synthese und Chlorameisensäureethylester‐Abbau von 6′‐Hydroxymethyl‐9‐methyllaudanosin

Prior

Wiegrebe

Sarıyar

1982

Archiv der Pharmazie

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Der CAE‐Abbau von cis‐5,8,13,13a‐Tetrahydro‐2,3,10,11‐tetramethoxy‐13‐methyl‐6H‐dibenzo[a,g]chinolizin (5) führt in Gegenwart von I⊝ zu dem Dibenz[c,g]azecin 19 und nicht zu einer Vorstufe der 6′‐Hydroxymethyl‐9‐methyllaudanosine 3, die aus 9‐Methylpapaverin durch Hydroxymethylierung, Quaternisierung und Boranat‐Reduktion erhalten wurden. Aus sterischen Gründen bilden sich mit CAE nur die Ethoxycarbonate 26, aber kein 3‐Phenyl‐4‐methyl‐isochroman 4. Auch aus dem Alkaloid Macrantalin (27) entsteht aus gleichem Grund kein 3‐Phenylisochroman: hier weicht die CAE‐Reaktion zum Stilben 28 hin aus. Beide Reaktionen stehen mit einem Inversions‐mechanismus an C‐1 bei der Umsetzung geeigneter 1‐Benzyltetrahydroisochinoline zu 3‐Phenyl‐isochromanen in Einklang.

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ChemInform Abstract: STUDIES IN SYNTHETIC PHOTOCHEMISTRY. PHOTOCHEMISTRY OF α‐KETO‐IMINES: A NOVEL SYNTHESIS OF XYLOPININE

Kessar¹,

Gupta²,

Singh³

et al. 1979

Chemischer Informationsdienst

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Photochemistry of α-keto-imines: a novel synthesis of xylopinine

Cited by 6 publications

References 0 publications

Generation and trapping of α-oxa and oxo o-quinodimethanes for natural product synthesis

Generation and trapping of α-oxa and oxo o-quinodimethanes for natural product synthesis

Synthese und Chlorameisensäureethylester‐Abbau von 6′‐Hydroxymethyl‐9‐methyllaudanosin

ChemInform Abstract: STUDIES IN SYNTHETIC PHOTOCHEMISTRY. PHOTOCHEMISTRY OF α‐KETO‐IMINES: A NOVEL SYNTHESIS OF XYLOPININE

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