Synthesis of multisubstituted halo-olefins via Pd-catalyzed cross-coupling reactions : applications in nucleoside chemistry (original) (raw)
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Chemistry – An Asian Journal, 2012
Reaction conditions for the CC cross-coupling of O 6-alkyl-2-bromo-and 2-chloroinosine derivatives with aryl-, hetaryl-, and alkylboronic acids were studied. Optimization experiments with silyl-protected 2-bromo-O 6-methylinosine led to the identification of [PdCl 2 (dcpf)]/K 3 PO 4 in 1,4-dioxane as the best condition for these reactions (dcpf = 1,1'bis(dicyclohexylphosphino)ferrocene). Attempted O 6-demethylation, as well as the replacement of the C-6 methoxy group by amines, was unsuccessful, which led to the consideration of Pdcleavable groups such that CC cross-coupling and O 6-deprotection could be accomplished in a single step. Thus, inosine 2-chloro-O 6-allylinosine was chosen as the substrate and, after reevaluation of the cross-coupling conditions with 2-chloro-O 6-methylinosine as a model substrate, one-step CC cross-coupling/deprotection reactions were performed with the O 6-allyl analogue. These reactions are the first such examples of a one-pot procedure for the modification and deprotection of purine nucleosides under CC cross-coupling conditions.
1,3- and 1,2-Unsaturated Derivatives as Valuable Synthetic Tools in Organometallic Syntheses
Current Organic Chemistry, 2010
This review gives an overview of our recent developments in the chemistry of 1,3-and 1,2butadiene derivatives, with a special attention to their use in palladium catalyzed reactions. The reactions of α,β-unsaturated and propargylic acetals with various lithium and mixed lithiumpotassium Schlosser reagents will be firstly reviewed. These processes have afforded (E)-1-alkoxy-1,3-dienes, and (E)-1,3-enynes, 1,3-diynes or allenes, respectively. When the reactions have been carried out in the presence of suitable electrophiles a linear route to functionalized derivatives has been set up. The above-mentioned compounds can be thus considered valuable synthetic tools for the construction of various and more complex structures and, in particular, they have been established to be useful reagents for the Suzuki-Miyaura cross-coupling reaction. As a matter of fact, alkoxy-functionalized butadienylboronic esters have been synthesized, cross-coupled with both N-protected and N-unprotected haloanilines (or halophenols), and finally transformed under mild conditions into quinolines and quinolinones (or chromenes and chromenones). The second part of the paper will deal with our recent interest in the Heck coupling of conjugate systems. In particular, the synthesis of γ-arylated α,β-unsaturated carbonyl compounds, by regioselective Heck process on 1-alkoxy-1,3-dienes in ionic liquids will be reviewed, in conjunction with the Heck coupling of 1,2dien-1-ols to α-arylated α,β-unsaturated aldehydes. A survey of the recent literature on closely related topics will complete the contribution.
Journal of Organic Chemistry, 1987
reported to give only p-anomers. The desired compound 3 was also the major product of glycosylation of the 6bromopurine 1, although the minor component was apparently the 9-CY isomer rather than the expected 7-0 isomer. In addition, the facile and direct isolation of the 9-P-deoxyribofuranosyl isomers precludes lengthy chromatographic separation of glycosylation products. In the final step, the protected 2,6-dihalo nucleosides are converted nearly quantitatively to the target 2-halo-2'deoxyadenosines. This chemical method appears to be adaptable to large-scale syntheses, as demonstrated by the 50-fold greater scale of the glycosylation of 2,6-dibromopurine as compared with the enzymatic glycosylation of 2-br0moadenine.~
Tetrahedron, 1994
Stereoisomerieally pure trisubstituted a$-unsaturated esters of general formula 7 have been efficiently synthetized using two different protocols. The fust one involves the palladium(0)/copper(I)-mediated cross-coupling reaction between alkyl(~-2-tributylstannyI-2-alkenoates, (E)-2, and aryl or alkenyl iodides. The second protocol, which allows to prepare stexeodefd L-a@, 2-methyl, 2-(1-nlkenyl) as well as 24cyl substituted a&unsaturated esters, is based on the cross-coupling reaction between easily available alkyl Q-or (E)-2-halo-2-akenoates and organostannanes in NMP, in the presence of catalytic amounts of Pdt&(PhCN),. A&It, and CuI. @)-and (E)-2ethenyl substituted a$-unsaturated esters prepared according to this procedure have been proven to be useful precursom to (Z)-and Q-a-ylidene-~butytolactones, Q-and (&It, respectively. Trisubstitutcd o$-unsaturated esters arc an important class of compounds as synthetic intcrmediatcs of many naturally-occurring substances. Stcrcoselcctive construction of such esters is a fundamental challenge in organic synthesis1 . In the context of our studies on the synthesis and applications of 1-alkenylstatmatres bearing a functional substituent in l-position, in 1992 we reported that stereodefined 2-(hetero)aryl substituted alkyl2alkenoates of general formula 1 could be efficiently prepared by a reaction sequence involving: (i) the palladium(O)mediated hydrostannylation of alkyl2Akynoates; (ii) iododestannylation of stereoisomerically pure alkyl (E)-2-tributylstannyl-2-alkenoates, (a-2, so obtained; and (iii) the palladium(O)-mediated reaction between the resulting alkyl Q-2-iodo-2-alkenoates, Q-3, and (&etero)arylzinc halidesz.
Tetrahedron, 1996
Stereodefined unsymmetrically 3,3-disubstituted alkyl 2-bromopropenoates, 5, were regioselectively prepared by Pd-mediated reactions between 3-alkyl, 3-aryl and 3-alkoxycarbonyl substituted (E)-2,3-dibromopropenoates, (E)-7. and aryl or l-alkynylzinc chlorides. The stereospecificity of these reactions was found to be dependent on the type of substituent present in the 3-position of (E)-7. The (E)-stemochemistry of compounds 5b, 5d and 5i so prepared was confirmed by their conversion into the corresponding 4-substituted 3-bromocoumarins. Tetrasubstituted or, It-unsaturated esters 10 were then synthesized by Pd-mediated reactions either of (E)-7 with a molar excess of an arylzinc chloride or an aryllributylstannane, or of a compound of general formula 5 with an aryitribntylstannane. An examination of the parameters which influence the stereochemistry and the yields of these arylations was made.
Cohalogenation of alkenes with DMF: an easy vicinal haloformyloxylation reaction
Journal of the Brazilian Chemical Society, 2007
A reação de alquenos com o ácido tricloro-isocianúrico ou N-bromo-sacarina ou I 2 / Fe 2 (SO 4) 3 na presença de DMF, seguida de tratamento em meio aquoso, leva à formação dos respectivos β-halo-formatos com alta regio-e estereosseletividade. The reaction of alkenes with trichloroisocyanuric acid or N-bromosaccharin or I 2 / Fe 2 (SO 4) 3 in the presence of DMF followed by aqueous work-up led to the corresponding β-haloformate in high regio-and stereoselectivity.