Presentation on theme: "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."— Presentation transcript:
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, 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? AuCl 3 $17,500/molPh 3 PAuCl $35,600/mol Pd(PPh 3 ) 4 $20,300/molPd 2 (dba) 3 $29,700/mol
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.
Pt(II) also works OK, but not as well and at higher temperatures Fukuda, Y.; Utimoto, K. Synthesis, 1991, 975.
and Au(I)? – yes, at least one example
Many trivial cases, such as hydration of alkynes, but….
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 alkenes are less reactive -exceptions….some activated alkenes
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
C-5 of the furan must be substituted, or else you a mixture of get two regioisomeric phenols
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.
Compare previous to… Why these do exo attack, as opposed to the previous endo attack, is not clear
Typical Au(I) catalysts (Ph 3 PAuCl) work, but are somewhat slower Nieto-Oberhuber, C.; Lopez, S.; Echavarren, A. M. J. Am. Chem. Soc. 2005, 127, 6178.