- Transition-Metal-Free Synthesis of Borylated Thiophenes via Formal Thioboration
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A simple, regiocontrolled, and transition-metal-free approach to access exclusively 3-borylated thiophene derivatives is reported. The commercially available B-chlorocatecholborane reagent (ClBcat) acts as a carbophilic Lewis acid to activate the alkyne i
- Bel Abed, Hassen,Blum, Suzanne A.
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p. 6673 - 6677
(2018/10/24)
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- Cyclobutene vs 1,3-Diene Formation in the Gold-Catalyzed Reaction of Alkynes with Alkenes: The Complete Mechanistic Picture
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The intermolecular gold(I)-catalyzed reaction between arylalkynes and alkenes leads to cyclobutenes by a [2 + 2] cycloaddition, which takes place stepwise, first by formation of cyclopropyl gold(I) carbenes, followed by a ring expansion. However, 1,3-butadienes are also formed in the case of ortho-substituted arylalkynes by a metathesis-type process. The corresponding reaction of alkenes with aryl-1,3-butadiynes, ethynylogous to arylalkynes, leads exclusively to cyclobutenes. A comprehensive mechanism for the gold(I)-catalyzed reaction of alkynes with alkenes is proposed on the basis of density functional theory calculations, which shows that the two pathways leading to cyclobutenes or dienes are very close in energy. The key intermediates are cyclopropyl gold(I) carbenes, which have been independently generated by retro-Buchner reaction from stereodefined 1a,7b-dihydro-1H-cyclopropa[a]naphthalenes.
- De Orbe, M. Elena,Amenós, Laura,Kirillova, Mariia S.,Wang, Yahui,López-Carrillo, Verónica,Maseras, Feliu,Echavarren, Antonio M.
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p. 10302 - 10311
(2017/08/09)
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- Flash Vacuum Pyrolysis of Stabilised Phosphorous Ylides. Part 4. Stepwise Construction of Terminal 1,3-Diynes, Conjugated Diacetylenic Esters and a Triacetylenic Ester
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Thirteen examples of stabilised alkynol ylides 6 have been prepared and are found, upon flash vacuum pyrolysis (FVP) at 500 deg C, to undergo extrusion of Ph3PO to give the diacetylenic esters 7 in moderate yield.At 750 deg C the same ylides afforded terminal 1,3-diynes 8 although often in poor yield.For R = 2-MeSC6H4 both 7 and 8 undergo secondary loss of Me* and cyclisation to give 2-alkynylbenzothiophene derivatives 9 and 10 in low yield.The first example of an alkadiynol ylide 11 has been prepared and is converted by FVP at 500 deg C into the triacetylenic ester 12.
- Aitken, R. Alan,Seth, Shirley
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p. 2461 - 2466
(2007/10/02)
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