Reactions of Trimethylsilyl Dienol Ethers with Palladium(II) Salts:  Formation of Formyl-Substituted η³-Allylpalladium Complexes and 4-Acyloxy-2-Alkenals

Abstract

Reaction of acyclic 1-(trimethylsilyloxy)-1,3-dienes with bis(acetonitrile)palladium dichloride, in benzene, affords formyl-substituted η3-allylpalladium complexes in good to excellent yield. In contrast, using palladium diacetate as the palladium(II) source produces 4-acetyloxy-substituted 2-alkenals. Excellent stereoselection in favor of the E-alkenal is usually observed. The corresponding benzoic acid esters can be prepared, with similar stereoselection, using 1-(trimethylsilyloxy)-1,3-dienes and palladium diacetate in the presence of an excess sodium benzoate.

Total Syntheses of Murrayamine E, I, and K

“…Treatment of prenal ( 14 ) with chlorotrimethylsilane and triethylamine in the presence of zinc chloride provided the silyl dienolate 20 . Oxidation of 20 with stoichiometric amounts of palladium­(II) acetate in the presence of sodium acetate afforded 4-acetoxyprenal ( 21 ) . 2-Hydroxy-3-methylcarbazole ( 22 ) was prepared from the arylamine 10b by our well-established palladium-catalyzed route .…”

“… a Reagents and conditions: (a) 1.1 equiv of TMSCl, 1.9 equiv of NEt 3 , 0.9 mol % ZnCl 2 , reflux, 25 h (ref ). (b) 0.85 equiv of Pd­(OAc) 2 , 0.85 equiv of NaOAc, MeCN, 40 °C, 3 h (ref ). (c) 1.2 equiv of 10b , 1.0 equiv of PhI, 5 mol % Pd­(OAc) 2 , 10 mol % SPhos, 1.4 equiv of Cs 2 CO 3 , PhMe, 100 °C, 26 h, 96%.…”

“…20 Oxidation of 20 with stoichiometric amounts of palladium(II) acetate in the presence of sodium acetate afforded 4-acetoxyprenal (21). 21 2-Hydroxy-3-methylcarbazole (22) was prepared from the arylamine 10b by our well-established palladium-catalyzed route. 10 Buchwald− Hartwig coupling 13 of iodobenzene and 10b, followed by palladium(II)-catalyzed oxidative cyclization, provided 2methoxy-3-methylcarbazole that has been isolated from natural sources by Bhattacharyya et al 22 Cleavage of the methyl ether afforded 2-hydroxy-3-methylcarbazole (22), which has been isolated from natural sources as well.…”

“…23 On the basis of our previous syntheses of non-oxygenated pyrano [3,2-a]carbazoles, 10 the pyran ring was annulated at 22 by a modification of Casiraghi's method. 10,14e,17 Reaction of 22 and 4-acetoxyprenal (21) in the presence of titanium(IV) isopropoxide provided a mixture of murrayamine K (8) and the carbazole 23. This mixture was immediately treated with methanolic potassium carbonate to provide exclusively 23.…”

“…Analogously, murrayamine I ( 7) was obtained by pyran annulation at the monoprotected 2,7-dioxygenated carbazole 13 (Scheme 5). Reaction of the carbazole 13 and 4acetoxyprenal (21) in the presence of titanium(IV) isopropoxide afforded a mixture of the silyl-protected murrayamine I 24 and the corresponding deacetyl derivative 25 in only low yield. However, treatment of 13 and 21 with substoichiometric amounts of phenylboronic acid and an excess of propionic acid (cf.…”