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Gold Chemistry of (Mostly) Alkynes

Gold Chemistry of (Mostly) Alkynes. Taken from 4 mini-reviews Hashmi, A. S. K. Gold Bull. 2003 , 35 , 3. Hoffmann-Roder, A.; Krause, N. Org. Biomol. Chem. 2005 , 3 , 387. Hashmi, A. S. K. Angew. Chem. Int. Ed. Engl. 2005 , 44 , 6990.

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Gold Chemistry of (Mostly) Alkynes

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  1. Gold Chemistry of (Mostly) Alkynes Taken from 4 mini-reviews Hashmi, A. S. K. Gold Bull.2003, 35, 3. Hoffmann-Roder, A.; Krause, N. Org. Biomol. Chem. 2005, 3, 387. Hashmi, A. S. K. Angew. Chem. Int. Ed. Engl. 2005, 44, 6990. Ma, S.; Yu, S.; Gu, Z. Angew. Chem. Int. Ed. Engl. 2006, 45, 200. General Points: 1) Most common oxidation states Au(I), and Au(III) -both are used, often do analogous things -are slightly different, and are probably not interconverting 2) Gold is too expensive, right? AuCl3 $17,500/mol Ph3PAuCl $35,600/mol Pd(PPh3)4 $20,300/mol Pd2(dba)3 $29,700/mol

  2. Why Gold? Au(I) and Au(III) are ‘soft’, carbophilic Lewis acids -particularly with alkynes -also allenes, and sometimes alkenes Original report Hutchings, G. H. J. Catal. 1985, 96, 292.

  3. Early Work - Heteroatom Nucleophilic Attack Pt(II) also works OK, but not as well and at higher temperatures Fukuda, Y.; Utimoto, K. Synthesis, 1991, 975.

  4. Nitrogen Nucleophiles, Contd. and Au(I)? – yes, at least one example

  5. Oxygen Nucleophiles Many trivial cases, such as hydration of alkynes, but….

  6. Functions Other Than Alkynes Alkynes are not the only C=C function whose reactions may be induced by Au(I) / Au(III), but there are the most commonly employed Allenes will also do much analogous chemistry, and in some cases alkenes will react too It is not clear that allenes are less reactive than alkynes (or more reacive, for that matter), but it is pretty apparent that alkenesare less reactive -exceptions….some activated alkenes

  7. Allenes

  8. Alkenes

  9. Carbon-Carbon Bond Formation In C-C bond forming reactions, Au(I) is more commonly encountered, perhaps even more than Au(III) The easy ones first – intramolecular reactions, presumably by the enol

  10. More Intramolecular Reactions Intermolecular Cases

  11. Multistep Processes C-5 of the furan must be substituted, or else you a mixture of get two regioisomeric phenols

  12. Enynes - Multistep Processes In most (but not all) cases, enynes react to undergo a non-obvious rearrangement of the carbon skeleton A gold carbene has been proposed as a central reactive intermediate Echavarren, A. M., et al Angew. Chem. Int. Ed. Engl. 2004, 43, 2402.

  13. Other Enynes Compare previous to… Why these do exo attack, as opposed to the previous endo attack, is not clear

  14. Vinyl/Arene Substituted Enynes Typical Au(I) catalysts (Ph3PAuCl) work, but are somewhat slower Nieto-Oberhuber, C.; Lopez, S.; Echavarren, A. M. J. Am. Chem. Soc. 2005, 127, 6178.

  15. More Conventional Multistep Cyclizations

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