Photochemische Reaktionen. 62. Mitteilung [1]. Die Photofragmentierung von O‐acetyljervin

Abstract

SociBt6 suisse de chimie, BBle -Societi svizzera di chimica, Basilea Nachdruck verboten -Tous droits r6servBs -. Printed by Birkhauser AG., Basel, Switzerland Erscheint 9mal jahrlich -ParaEt 9 fois par an 43. Photochemische Reaktionen 62. Mittellung [l] Herrn Professor Dr. Hans-Herloff I9zhoffeen zu seinem 65. Geburtstag gewidmct (30. XT. 70)Summary. On ultraviolet irradiation 0-acetyljervine (1) is subjected to several parallel fragmentations. From the complex reaction mixtures obtained in a variety of solvents (dioxan, tetrahydrofuran, acetonitrile, iso-octane, benzene) the major alicyclic products 6-8 and the heterocyclic compounds 12-16 have been isolated. Products 6-8 undergo further photochemical changes, e.g., decarbonylation of 7 to 9 and hydrolytic cleavage of 8 to 10.These photofragmentations are initiated almost specifically upon selective n + n* excitation at 2537 A with a quantum yield of @2537 = 0.145 for conversion of starting material. Reaction upon irradiation in the long-wavelength n --f n* absorption band is very much less efficient (@366" = 0.611 . both determinations for 0-trimethylsilyl-jervine (2) in tetrahydrofuran). A high degree of photostability IS observed also at 2537 A on N-protonation of 0-acetyljervine (1) in acetic acid. Furthermore, reactivity is greatly reduced for the N-methyl (3) and N-acetyl (4) derivatives in neutral solvents a t 2537 A. N-Chloro-0-acetyljervine (5) in dioxan a t 2537 h gave preferentially 0-acetyljervine hydrochloride. Resultate der UV.-Bestrahlungen. -0-Acetyljervin (1 [3] ; uv. in Athanol: ~~~ -12'200, E:& = 50; in Benzol: E:& = 54) wird bei der Bestrahlung mit Licht von 2537 A mehreren parallel ablaufenden Abbaureaktionen unterworfen2), die zu stickstoffreien, den Ringen A-D von 1 entsprechenden Spaltprodukten sowie stickstoffhaltigen Verbindungen fuhren. Von den ersteren wurden die Hauptprodukte 6 [5], 7 und 8 isoliert (Formelschema 1). Diese Verbindungen sind unter den angewandten Bestrahlungsbedingungen ebenfalls photolabil. Der qualitative diinnschichtchromatographische Produktnachweis bei Versuchen mit 1 in analytischem MaBstab zeigte, dass 6, 7 und 8 bei der Verwendung verschiedenster Losungsmittel wie Dioxan, Tetrahydrofuran, Acetonitril, Isooctan und Benzol entstehen. In praparativen Ansatzen in Dioxan mit 2537 A wurden folgende ungefahre Hochstausbeuten erzielt (berechnet auf umgesetztes Ausgangsmaterial) : 16% 6 , 22% 7 und 11% 8.Es ist dabei aber zu berucksichtigen, dass bei der zur Reindarstellung erforderlichen wiederholten Chromatographie an Kieselgel jeweils betrachtliche Verluste in Kauf genommen werden mussten. E 2 5 2l ) 2)Auszugweise der Dissertation Bozzato [2) entnommen.Ein Teil dieser Resultate wurde bereits in Kurzmitteilungen und Ubersichtsrcferaten (41 veroffentlicht. 27a 430 HELVETICA C,HIMICA ACTA -Vol. 54, Fasc. 2 (1971) -Nr. 43 h v --R'O 6 RO &'"" li 7 1 R'=Ac.R"=H 2 R' =(CH,),Si, R"=H 3 R = A c . R = C H 3 4 R'=R=Ac 5 R'=Ac, R = C I R =Ac bzw. (CH,),SI Formelschema 1. Photolyse von 0-Acetyl-(1) und 0-2'rimeth~~lsilyZ-jervin ...

Synthetic Aspects of the Di-π-methane Rearrangement

“…However, the usual photoreactivity reported for the majority of β,γ-unsaturated aldehydes, until very recently, was decarbonylation. Thus, Schaffner et al demonstrated in a series of reports, published almost 20 years ago, that β,γ-unsaturated cycloalkenyl aldehydes 162 and 163 ,137b steroidal β,γ-unsaturated aldehydes 164 , 165 , and 166 and the β,γ-unsaturated aldehyde with an exocyclic double bond 167 137b underwent decarbonylation on direct irradiation. The triplet-sensitized reactivity of aldehyde 163 was also investigated.…”

“…Again, under these conditions, decarbonylation took place. Triplet-state photoreduction to alcohol and homologization to the corresponding methyl and ethyl ketones were observed on direct irradiation of aldehyde 168 137b direct or acetophenone-sensitized irradiation of aldehydes 169 gave two products resulting from decarbonylation and 6-electron cyclization of the cis -stilbene type.…”

Photochemistry of alkaloids

“…Irradiation26 of berberium chloride (90) in the presence of oxygen gave 8-methoxyberberine phenol betaine (91) which is a precursor for the synthesis of (±)-a-and (±)-/3-hydrastine, (±)-ophiocarpine, and (±)-13-epiophiocarpine. The photo-oxygenation27 of berberinium betaine (92) (>0.1 % concentration) gave the epidioxydibenzoquinolizidine (93) while at <0.1% concentration, the photoproduct berberal (94) was isolated from the reaction mixture. The photolysis of 13-oxotetrahydroprotoberberine (95) in the presence of sodium hydride and ethanol under nitrogen atmosphere resulted in the formation of a spirobenzylisoquinoline (96) in 45% yield.…”

Cycloaddition Reactions of Chiral 2-Amino-1,3-butadienes with Nitroalkenes: Synthesis of Enantiomerically Pure 4-Nitrocyclohexanones1

“…To establish the absolute configuration of the stereogenic center of compounds 6 and 7 , compound 7c was transformed into pyrrolidinone 12 , a previously described compound with known absolute configuration and optical rotation value (Scheme ). With this purpose, the amino group of 8 was Boc-protected by treatment with (Boc) 2 O in CH 2 Cl 2 .…”