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81.
Iñaki Osante 《Tetrahedron letters》2004,45(6):1253-1256
C-12b substituted isoindolo[1,2-a]isoquinolones 4 are prepared efficiently via a tandem Parham cyclisation--α-amidoalkylation reaction. Thus, Parham cyclisation on imide 1 generates a 12b-hydroxy isoindolo[1,2-a]isoquinolone, which is an immediate precursor of an N-acyliminium ion. Intermolecular alkylation with different π-nucleophiles (allyl silanes or enol ethers) is accomplished upon treatment with Lewis acids (BF3·OEt2, TiCl4) to obtain nuevamine-type derivatives in high yields (69-95%) under mild conditions. 相似文献
82.
A silyl substituted cyclopentene was prepared from acyclic triethylsilyl pentenol derivatives via palladium-catalyzed 5-endo-trig process. 相似文献
83.
The lithiation of 4-heterosubstituted dibenzothiins 1 (phenoxathiin, phenothiazine and thianthrene) with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 7.5% molar) in THF at temperatures ranging from −90 to −78°C gives the corresponding functionalised organolithium intermediate I, which by reaction with different electrophiles [H2O, D2O, ButCHO, PhCHO, Ph(CH2)2CHO, Me2CO, Et2CO, (CH2)5CO, (CH2)7CO] at the same temperature, followed by hydrolysis, gives the expected functionalised thiols 2. Cyclisation of some thiols 2 under acidic conditions leads to the corresponding seven-membered dibenzo heterocycles 5. In the case of thianthrene 1c, after addition of a carbonyl compound as the first electrophile [MeCHO, ButCHO, Me2CO, Et2CO, (CH2)5CO], the corresponding intermediate II can be lithiated again and react with a second electrophile. Diols 3 are obtained after hydrolysis when a carbonyl compound [ButCHO, PhCHO, Ph(CH2)2CHO, Me2CO, Et2CO, (CH2)5CO] is used as the second electrophile. Acidic cyclisation of diols 3 gives substituted phthalans 6 in almost quantitative yields. Finally, in the case of using carbon dioxide as the second electrophile, phthalides 4 are obtained after acidic hydrolysis. 相似文献
84.
S. V. Kessar 《Journal of Chemical Sciences》1988,100(2-3):217-222
KNH2/NH3 cyclisations of some alkoxy substituted arylhalides proceed in poor yields. This shortcoming may be overcome by the use of
LDA/THF to effect the ring closure which may occur through benzyne or radical intermediates. Besides ortho halogenated dihydroanils
and amides, the cyclisation of the benzylamine Schiff bases also provides a convenient route to isoquinoline alkaloids. 相似文献
85.
Efficient 6-endo-trig free radical cyclisations of various 3-phenyl-acryl enamides to piperidin-2-ones, by using Bu3SnH and AIBN in boiling toluene, are reported. A different result has been observed for related enamide system without phenyl substituent at the 3-position of an acrylic moiety, as such a reaction of 3-methyl-butenoic acid cyclohex-1-enyl-methyl-amide afforded only the 5-exo-trig product. The difference in the cyclisation mode has been explained in terms of a reversible process leading to the thermodynamically more stable product. An application of this method for the tandem cyclisation permits to obtain idolizidine derivatives. 相似文献
86.
The substitution of symmetrical N-protected diketopiperazines (DKPs) via enolate intermediates has been studied. The enolate reactions were highly diastereocontrolled, leading to enantiopure DKP products if chiral amino acid precursors were employed, and giving racemic products, starting with centrosymmetric DKPs, even when a chiral lithium amide base was used to generate the lithium enolate. With unsymmetrical DKPs derived from proline and either alanine, phenylalanine or valine, the enolate substitution occurred with high regio- and stereoselectivity on the proline residue. This enabled the synthesis of substituted DKPs that could be cyclised via cationic processes to give the bicyclo[2.2.2]diazaoctane core structure present in paraherquamide and stephacidin natural products. 相似文献
87.
J.S. Yadav N. Thrimurtulu K. Uma Gayathri B.V. Subba Reddy A.R. Prasad 《Tetrahedron letters》2008,49(47):6617-6620
Syntheses of xestodecalactone C and epi-sporostatin are described utilising Prins cyclisations, Mitsunobu reaction and intramolecular Friedel-Crafts acylation. The approach is convergent and highly stereoselective. 相似文献
88.
A mild and efficient protocol for the synthesis of chromanols has been elaborated via an arginine-mediated cascade cyclisation reaction between salicylaldehyde and methyl vinyl ketone in water. Various substituted salicylaldehydes were successfully used in the aqueous based reaction, affording the chromanol adducts in very good yields. Mechanistically, the reaction presumably proceeds via an oxa-Michael addition followed by an intramolecular aldol addition pathway; the lack of stereoselectivity in the formation of the chromanols alludes to a non-covalent interaction of the amino acid with the substrates as the most plausible interpretation for the activation. 相似文献
89.
《Comptes Rendus Chimie》2014,17(12):1165-1168
In the course of the Lewis acid-mediated cycloaddition of 1,8-bis(trimethylsilyl)-2,6-octadiene to bis-ketals, we have observed an unprecedented retro-Claisen condensation from the ketalisation of a 3-hydroxy-2,4-pentadione giving rise to a substituted 2,2,3-trimethoxybutane and an anti-Markovnikov stereoselective cycloaddition of the 1,8-bis(trimethylsilyl)-2,6-octadiene to this latter ketal. 相似文献
90.
Synthesis of Methylene‐Bridged Biscarbazole Alkaloids by using an Ullmann‐type Coupling: First Total Synthesis of Murrastifoline‐C and Murrafoline‐E
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Sebastian K. Kutz Dr. Carsten Börger Dr. Arndt W. Schmidt Prof. Dr. Hans‐Joachim Knölker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2487-2500
We describe the total synthesis of methylene‐bridged biscarbazole alkaloids by using a late‐stage Ullmann‐type coupling of fully functionalised carbazole subunits. The carbazole derivatives were synthesised via a sequence of palladium(0)‐ and palladium(II)‐catalysed coupling reactions. Our approach has provided bismurrayafoline‐A, bismurrayafolinol, chrestifolines B–D, and the first total synthesis of murrastifoline‐C and murrafoline‐E. 相似文献