Radical Hydrostannylation, Pd(0)-Catalyzed Hydrostannylation, Stannylcupration of Propargyl Alcohols and Enynols: Regio- and Stereoselectivities (original) (raw)
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The Journal of Organic Chemistry, 2003
A study on the addition of trineophyltin hydride (1) to alkynones under free radical (AIBN and Et 3 B) and palladium-catalyzed [(PPh 3 ) 2 PdCl 2 ] conditions is reported. The results obtained indicate that the addition of 1 to eight ynones catalyzed by bis(triphenylphosphine)palladium(II) chloride led in all cases to addition products in very high yields (80-96%). These additions take place with excellent regio-and stereochemistry, leading to the R adducts as major products in seven out of the eight cases studied. Also the E adducts, resulting from a syn attack, were the only (seven cases) or the predominant (one case) products. The radical hydrostannations initiated by AIBN of ynones 2-5 with 1 led to addition products in good yields (60-88%); with the more hindered ketones 6 and 7-9 the yields obtained were lower. The radical additions initiated by triethylboron to ynones 2-6 follow a similar pattern but with lower yields; no addition products in the hydrostannation of ynones 7-9 were detected. The new acyl-substituted vinylstannanes, owing to their greater stability compared with that of their tributyl-and trimethylstannyl analogues, can be purified by column chromatography using neutral alumina (in all cases) or silica gel 60 (in most cases) as adsorbents. Full 1 H, 13 C, and 119 Sn NMR data are given.
ChemInform, 1992
Vinyl tril]ates react ~ith ['r-substituted-,t,l~-unsaturatcd aldehydes, ketones, and esters in the presence of catalytic amounts ol Pd(OAc) 2 and an excess ol KOAc, omitting phosphinc Iigands, to give xinylic substitution pr~xlucts in g~od to high yield ,,s ith high regioselectix it3,. The added ,,in)l unit is prcferentiall3 linked to the [~-carbon atom. As to the stere<vchemistr 3, ',in}lie substitution pr~x.lucts contain the carbon31 group on the same side of the preexisting [~-substilucnt. The use ol KOAc has been proxcd to bc superior tx~th to tcrtiarx amines and to carbonate or bicarbonate bases with or ss ithout the addition of salts such as LiCI and n-Bu4NCI. The application ol the reaction to the s) nthesis of a cardenolidc derix atixe ~s reported. Depending on the nature ol ~substituted-~t,~unsaturated carbonvl coml:xmnds, the reaction can prc~duce h.vdr~xin31ation (formal conjugated addition)products
Syntheses and Applications of Vinylstannanes
2009
The development of methods for the synthesis of vinylstannanes is reported. The applications of these useful compounds are highlighted in a variety of total syntheses of natural products. Cyclic and acyclic vinylstannanes were prepared conveniently in a simple one-pot procedure from the corresponding ketones. The scope of ketones was illustrated and the limitations were highlighted. Moderate to high yields of vinylstannanes are reported that compare favourably with other methods. Two cases of unsymmetrical ketones provided the less substituted vinylstannanes. A straightforward purification procedure was developed for non-polar vinylstannanes that allowed for the separation from Bu 3 SnH contamination. Trans-1-stannyl-1-alkenes were prepared in high regioselectivity (95:5, trans:gem) from unhindered 1-alkynes by using Pd 2 dba 3 /Cy 3 PHBF 4 /i-Pr 2 NEt on a wide range of terminal alkynes. This system exhibited higher selectivities and yields for trans-vinylstannanes than the original PPh 3-based catalysts that are widely adopted. Contrary to popular belief, it was found that ligands have a dramatic effect on the regioselectivity of palladium-catalyzed hydrostannations of 1-alkynes. Steric and electronic arguments were used to explain the observed regioselectivities. An insect sex pheromone was synthesized using the hydrostannation methodology that was developed. An inseparable 95:5 mixture of trans and geminal vinylstannanes did not pose a problem during the synthesis, as the geminal isomer did not participate in the Stille coupling. Chapter 1 references……………………………………………………………348 Chapter 2 references……………………………………………………………350 Chapter 3 references……………………………………………………………352 Chapter 4 references……………………………………………………………355 Chapter 5 references……………………………………………………………357 Chapter 6 references……………………………………………………………359 APPENDICES………………………………………………………………………362 APPENDIX A: X-RAY CRYSTALLOGRAPHIC DATA OF 6-114……..362 APPENDIX B: X-RAY CRYSTALLOGRAPHIC DATA OF 6-135……..369 APPENDIX C: X-RAY CRYSTALLOGRAPHIC DATA OF 6-142……..375 APPENDIX D: X-RAY CRYSTALLOGRAPHIC DATA OF 6-143……..381 xx List of Tables Chapter 1 More recently, cross-coupling reactions have garnered a great deal of attention due to their versatility in forming new carbon-carbon bonds. Kosugi et al. were able to accomplish the first cross coupling reaction involving tin (Scheme 1.5). 7 Scheme 1.5 Cross coupling reaction between aryl halides and allylstannane proceeded by applying catalytic amounts of palladium (0). Milstein and Stille also demonstrated a cross coupling reaction between acyl chlorides and tetraalkyltin compounds (Scheme 1.6). 8 Scheme 1.6 Cross-coupling reactions involving tin are generally known as the Stille coupling. These illustrated reactions serve as the basis for many important organic synthetic methods.
Organic Letters, 2008
General Experimental Glassware used for hydrostannations was treated with hot aqua regia (conc. HCl: conc. HNO 3 , 3:1 v/v) then rinsed with distilled water to remove traces of palladium. All reactions were performed using flame-dried glassware under an argon atmosphere. Dichloromethane and diisopropylethylamine were freshly distilled from calcium hydride. Tetrahydrofuran, diethyl ether, and toluene were freshly distilled from sodium/benzophenone. Tributyltin hydride was prepared by reduction of bis(tributyltin)oxide with NaBH 4 in ethanol 1 and was distilled (kugelrohr) before use. Samples were checked by 13 C NMR spectroscopy (in C 6 D 6 since Bu 3 SnH reacts with CDCl 3) for the presence of Bu 3 SnSnBu 3 and were re-distilled if necessary. 2 Other reagents were purchased from Sigma-Aldrich and used without further purification except t-Bu 3 PHBF 4 and t-Bu 2 PCH 2 t-BuHBF 4 which were gifts from FMC Lithium Co. 10-Undecyn-1-ol (1b) was prepared by bromination/dehydrobromination of 10-undecen-1-ol, 3 commercially-unavailable propargylic alcohols were prepared by addition of lithium trimethylsilylacetylide to the appropriate aldehyde followed by treatment with K 2 CO 3 /MeOH, 4 and alkyne 1n was prepared according to a literature procedure. 5 1 H and 13 C NMR spectra were recorded in CDCl 3 at 300 MHz and 75 MHz, respectively, unless otherwise noted. Mass spectra were recorded on a Kratos MA890 mass spectrometer using electron impact (EI, 70 ev) ionization unless otherwise specified. General procedure for hydrostannation of alkynes: Pd 2 dba 3 (4.6 mg, 0.005 mmol), tricyclohexylphosphonium tetrafluoroborate (7.4 mg, 0.02 mmol) and diisopropylethylamine (5.2 mg, 0.04 mol) were added successively to toluene (10 mL)
Cyclization Reactions of Allylic O-Stannyl Ketyls
Journal of Organic Chemistry, 1995
This is a summary of an investigation of the tributyltin hydride-induced cyclization reactions of unsaturated ketones with electronically deficient olefins. This reaction was initiated by an 0-stannyl ketyl formed by the addition of a tributyltin radical to a carbonyl, which has both anionic and radical character. The intramolecular coupling produced functionalized cyclopentanes, bearing two synthetically useful carbon appendages. An activating or electron-withdrawing function on the alkene was essential to the cyclization. A dilution study revealed that excellent anti stereoselectivities ('50:l) could be achieved, and this was attributed to a reversible cyclization. Another goal of this study was to separate the radical reactivity from the anionic reactivity of the 0-stannyl ketyl by the participation of labile functional groups and external electrophiles. The presence of minor products and enolate-trapping studies demonstrated that the anionic character of the ketyl could be utilized in the form of a tin enolate. This work represents the first free radical-and reagentbased approach to the study of the intramolecular hydrodimerization of activated alkenes. ( 5 ) (a) Sugawara, T.; Otter, B. A.; Ueda, T.
Stereoselective hydrostannation of substituted alkynes with trineophyltin hydride
Journal of Organometallic Chemistry, 2002
This paper reports the results obtained in a study on the radical hydrostannation of mono-and disubstituted alkynes with bulky triorganotin hydrides using triethylborane as initiator. The addition of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), and 9-tripticyldimethyltin (3) hydride to eight alkynes was carried out at room temperature leading to vinylstannanes in good to excellent yields and, mostly, with complete stereoselectivity. The results obtained in a study on the relative reactivity of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), 9-triptycyldimethyltin (3) hydrides, and tri-n-butyltin hydride (29) using the radical reactions between these hydrides and 6-bromo-1-hexene (28) are also reported. Full 1 H-, 13 C-, and 119 Sn NMR characteristics are included.
Journal of Organometallic Chemistry, 2006
This paper reports the results obtained in a study on the radical hydrostannation of mono-and disubstituted alkynes with bulky triorganotin hydrides using triethylborane as initiator. The addition of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), and 9-tripticyldimethyltin (3) hydride to eight alkynes was carried out at room temperature leading to vinylstannanes in good to excellent yields and, mostly, with complete stereoselectivity. The results obtained in a study on the relative reactivity of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), 9-triptycyldimethyltin (3) hydrides, and tri-n-butyltin hydride (29) using the radical reactions between these hydrides and 6-bromo-1-hexene (28) are also reported. Full 1 H-, 13 C-, and 119 Sn NMR characteristics are included.