Umwandlungen der Ketoxidoverbindungen; Bildung von β‐Keto‐aldehyden aus α,β‐ungesättigten Ketonen

Abstract

2-n. NaOII. Es bilden sich amBoden des GefaIjes farblose, dickfliissig-sohaumige Oltropfen, welche Sauerstofl entwickeln (konz. LSsung von Natriumsuperosyd). Am andern Tage haben sich 2 Arten ,von farblosen Krystallen abgeschieden : i n der Hauptmenge Prismen, daneben sechseckige Tiifelchen I). Man saugt ab und wiischt erst mit Alkohol. Wascht man dann mit Wasser nach, so losen sich die Tafelchen, und nur die Prismen bleiben zuriick in einer Ausbeute von 0.75 g. Durch Umkryatallisieren aus etwa 45 Tlo. heisen Alkohols erhiilt man Prismeo r o o Schmp. 167-1680. 0.2179 g Sbst.: 0.6518 I: COP, 0.0934 g HIO. Cg3RL6O1. Ber. C 81.2, IEI 4.7. Gef. a 81.5, D 4.8. Bei Einwirkung von nur 2 Mol. HaOS auf das doppclt ungesiittigte Keton (I g in 100 g Alkobol, 2 ccni 15-proz. HzOa, 4 ccm 2-n. NaOU) entstand ein viel leichter liislichcs, erst (lurch Wasser ausxufiillendes Produkt, das sehr niedrig (unterhalb 600) scbmols und schwer zu krystallisieren war.Halle a. S., J u l i 1921. Ernst Weits und Alfred SohePfer: Urnwandlungen der Ketoxidoverbindungsn; Bildung won 8-Keto-aldehyden au8cr,B-ungesitttigten Ketonen.

Total Syntheses of Crinipellins Enabled by Cobalt‐Mediated and Palladium‐Catalyzed Intramolecular Pauson–Khand Reactions

“…Thecompound 16 a has all the essential functional groups of 1 except the methylene group at C3, therefore we performed am odified Eschenmoser methylenation by reaction of 16 a with N-methylanilinium trifluoroacetate and paraformaldehyde in THF at 70 8 8Ct og ive (À)-crinipellin A [(À)-1]i n8 6% yield. 1 HNMR, 13 CNMR, and optical rotation data of synthetic (À)-1 were in good agreement to those reported in the literature. [2a] We next explored the total synthesis of (À)-2 from 16 b.…”

“…[10] Implementation of this approach required the enyne ester 9,w hich was prepared by the Tr ost protocol [11] from known compound (R)-4-isopropyl-3-methylcyclohex-2-en-1-one (6) as prepared prepared in four steps from commercially available 4-isopropyl-3-methylphenol (5). [12] In the event, 6 underwent adiastereoselective Weitz-Scheffer-type epoxida-tion, [13] and the resultant ketone 7 was condensed with p-NO 2 ArSO 2 NHNH 2 and subsequently treated with NaHCO 3 to initiate Eschenmoser fragmentation [14] to afford the acetylene ketone 8 in 68 %y ield. In the preparation of 9, 8 was first subjected to aW ittig reaction, and the resultant enyne,w ithout workup,w as directly treated with BuLi and ethyl chloroformate sequentially to afford 9 in 75 %y ield.…”

Enantioselective Formal C(sp2)−H Vinylation

“…After completion of the vinylogous Michael addition (as ascertainedbyTLC), the reaction solvent was replaced by THF and the reaction mixture treated with DBU at 0 8C( see the Supporting In- The expediency of this protocol was illustrated by elaboration of the C(sp 2 )ÀHv inylated product 7aa to an umber of potentially useful compounds (Scheme 6). For example, ar egio-and diastereoselective reduction of 7aa under Luche conditions [18] furnished the allylic alcohol 8 in 93 %y ield, essentially as as ingle diastereoisomer.W eitz-Scheffer-type epoxidation [19] of 7aa provided epoxycyclopentanedione 9,o nce again, as as ingle diastereoisomer in 74 %y ield. The application of 7aa as an electrondeficient diene is demonstrated by Diels-Alder reaction with in situ-generated benzyne as the dienophile.…”

“…For example, a regio‐ and diastereoselective reduction of 7 aa under Luche conditions furnished the allylic alcohol 8 in 93 % yield, essentially as a single diastereoisomer. Weitz–Scheffer‐type epoxidation of 7 aa provided epoxycyclopentanedione 9 , once again, as a single diastereoisomer in 74 % yield. The application of 7 aa as an electron‐ deficient diene is demonstrated by Diels–Alder reaction with in situ‐generated benzyne as the dienophile.…”

NAD(P)H‐Independent Asymmetric CC Bond Reduction Catalyzed by Ene Reductases by Using Artificial Co‐substrates as the Hydrogen Donor

“…In addition to the typical ene reductase activities, OYEs also show NAD(P)H oxidase activity, in the course of which H 2 O 2 is generated through oxidation of reduced FMNH 2 by molecular oxygen. Depending upon the type of substrate, hydrogen peroxide thus formed may cause spontaneous Weitz–Scheffer epoxidation of the activated CC bond,19, 20 which can be prevented by working under an inert atmosphere 21…”