SummaryEsters of carboselenoic acids, formed from carboxylic acids by conventional methods, undergo reaction with tributyltin hydride in inert aromatic solvents, either by heating to give the corresponding aldehyde or the corresponding alkane depending on reaction temperature and the structure of the parent carboxylic acid, or by ultraviolet irradiation at ambient temperature when the aldehyde is formed predominantly in high yield. In the case of esters of a,P-unsaturated carboselenoic acids the thermal reaction leads only to the corresponding aldehyde.The above stannane reduction can also be applied to selenocarbonates of primary and secondary alcohols (prepared from the corresponding chloroformates), to give the alkane, the parent alcohol and the corresponding formate, in relative amounts depending on the reaction temperature.These reactions thus constitute preparatively useful and high-yield degradation methods compatible with the presence of many other functional groups.In connection with our work on the synthesis of quassinoid bitter principles [2] we have described in a previous publication [1] an example of what appeared to be a novel possible route for the degradation of a carboxylic acid to the corresponding nor-alkane (Scheme 1). Carboxylic acid 1 was converted via its chloride 2 into the phenylcarboselenoate 3. When this was heated with tributyltin hydride in benzene at 80" the 8 P-methyl derivative 4 (product of reductive decarbonylation) and the alkenyl hemiacetal 5 (derived from the expected aldehyde, see 1, X=H) were produced in about equal amounts.In this paper we demonstrate that the radical-induced stannane reduction of phenyl carboselenoate a can lead to either aldehydes b or nor-alkanes c as main products, depending on temperature (Scheme 2). In addition we shall describe the I)Part 261, see [l].

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Mitteilung [l]Szimmary : In addition to the preliminary communication Ll] a detailed description of the first partial synthcsis of steroidal alkaloid batrochotoxinin A (1) is presented. Zwischen 1963 und 1969 berichteten Witkop et al. uber die Isolierung der drei Steroidalkaloide Batrachotoxinin A (l), Batrachotoxin ( 2 ) und Homobatrachotoxin (3) aus der Haut des kolumbianischen Pfeilgiftfrosches Phyllobates aurotaeizia [2] [3] [4] [5] sowie iiber die rontgenographische Strukturaufklarung des Grundkorpers 1 [4] [6] und dessen Uberfuhrung in die Pyrrolester 2 und 3 151. Die ungewohnliche, ausserordentlich komplexe Struktur von Batrachotoxinin A (1) sowie die hohe Toxizitat l) bei gleichzeitig bemerkenswerten pharmakologisclien Eigenschaften z, veranlassten uns 1969 zur Aufnahme voii Studien zur partialsynthetischen Erschliessung des aus naturlichen Quellen nur sehr schwer zuganglichen Grundkorpers Batrachotoxinin A (1). In1 Rahmen dieses Arbeitsprogrammes berichteten wir seither uber die Darstellung der Modellverbindungen 10 [8] [9], 16 [lo], 26 1111, 35 [I21 [13] (141 und 46 [14],

1) CH31, K O t W THPO2) H30* 3 4 dass durch Akylierung eines 7-0~0-13,17-secosteroids (vgl. 3, Schema I) mit Methyljodid und starker Base die essentielle 8P-Methyl-Grlrppe nicht eingefiihrt werden kann. Als Alkylierungsprodukte wurden lediglich 8 a-methylierte Verbindungen erhalten (vgl. 4). In der vorliegenden Arbeit wird hingegen gezeigt, dass die photochemisch induzierte [2 + 21-Cycloaddition von Allen an das vinyloge a -H,ydroxyketon 5 (Schema 2) das 8 p, 14P-konfigurierte Cyclobutanderivat 6 ergibt, das zur Schlusselverbindung 7 mit 8 P-konfigurierter Methylgruppe abgebaut werden kann. Die Verbindung 6 ist ebenfalls ein geeignetes Zwischenprodukt fur die partialsynthetische Erschliessung der pharmakologisch interessanten quassinoiden Verbind~ngen~) vom Typus des Bruceantins (8) mit 8 P-Hydroxymethylgr~ppe~). 6 7Synthese der Schliisselverbindung 7. -In Anbetracht der starken Funktionalisierung im Bereiche der Ringe B und C des Quassins (1) schien es angebracht, den Ring A zunachst derart zu gestalten, dass die Diosphenolathergruppierung in diesem Ring in wenigen, voraussehbar problemlosen Schritten am Ende der Synthese hergestellt werden kand). Zu diesem Zwecke eignet sich vor ailem ein 1,2,3-Trihydroxy-4 a-methylandrostanderivat mit einer 1,2-trans; 2,3-cis-Anordnung der 4,Vgl. dazu [6]. 5, ,Fur weitere synthetische Arbeiten auf dem Gebiete quassinoider Bitterstoffe vgl. [2] und [7]. Fur eine alternative Synthese des Ringes A in einem Androstanmodell vgl. [2]. 16) Eine Losung von 1, OOO g Diphenyldiselenid in 6,4 ml THF wurde mit 2,6 ml ca. 50proz. unterphosphoriger Saure unter Nz unter Ruckfluss erhitzt. Nach 20 Min. hatte sich die Losung vollig entfarbt. Unter einem N2-Strom wurde die abgekuhlte Mischung mit 25 ml Benzol ausgeschuttelt, die organische Phase mit Magnesiumsulfat getrocknet und luftdicht abgeschlossen im Kuhlschrank aufbewahrt.

SummaryTreatment of the (Z)-isomers 6 and 7 of the four isomeric 16-acetoxy-17-hydroxyimino-steroids 6-9 with DCC/DMSO/CF,COOH (Moffaat fragmentation of oximes) yielded the seco-a-acetoxy-nitriles 10 and 11, respectively, while similar treatment of both (E)-isomers 8 and 9 gave the formyl-carbonitrile 14. The mechanism of these fragmentations is discussed. ',C-NMR. data of oximes are presented which show the y-gauche effect being associated with (T (C-H)-bond polarization.Moflat et al.[3] have shown that 17-hydroxyimino-steroids such as 1 on treatment with dicyclohexylcarbodiimide (DCC), dimethylsulfoxide (DMSO) and trifluoroacetic acid (TFA), are converted into seco-nitriles such as 2 in good yields (Scheme 1). In order to account for the unusually high yield of the Beckmann-IIreaction product (e.g. 2) these authors have proposed an eightmembered ring cyclic-fragmentation mechanism (see A), without, however, going into the question of the effect of oxime (E/Z)-configuration on their suggested scheme.In connection with a natural product synthesis we have had occasion to apply this fragmentation reaction to the four isomeric 16-acetoxy-17-hydroxyiminosteroids 6-9 whose configuration could be unambigously assigned'). Both (Z)-isomers 6 and 7 were found to give the seco-a-acetoxy-nitriles 10 and 11, respectively, each in about 40% yield, together with the Beckmann-I-rearrangement products, 12 and 13, respectively, also in about 40% yield. From the (E)-isomers 8 and 9 there were obtained the hydrolysis products 4 and 5, respectively, together with the unstable formyl-carbonitrile 14 which was formed in variable amounts*). I) 2,Compounds 6-9 have been prepared by standard methods from 3 via 4 and 5 by Pb(OAc)4, Ac2O oxidation and NH20H. HC1 treatment in pyridine solution, respectively (see [2] and Table). The absence of product 14 from the fragmentation of 6 and of 7, and the absence of 10-13 from the fragmentation of 8 and of 9 indicates that the starting materials are configuratively stable under the conditions employed. Moreover, configuratively unchanged starting material was isolated from the reaction mixture to the extent of 5-10%.