| Lanthanide-organic complexes of the general type Ln[N(SiMe3) 2]3 (Ln = La, Sm, Y, Lu) serve as effective precatalysts for the rapid, exo-selective, and highly regioselective single and tandem double intramolecular hydroalkoxylation/cyclization of primary and secondary alkynyl alcohols and dialkynyl dialcohols to yield the corresponding exocyclic enol ethers.;For single intramolecular hydroalkoxylation/cyclization, conversions are highly selective with products distinctly different from those generally produced by conventional transition metal catalysts, and turnover frequencies as high as 52.8 h-1 at 25°C are observed. The rates of terminal alkynl alcohol hydroalkoxylation/cyclization are significantly more rapid than those of internal alkynyl alcohols, arguing that steric demands dominate the cyclization transition state. The hydroalkoxylation/cyclization of internal alkynyl alcohols affords excellent E-selectivity. The hydroalkoxylation/cyclization of the SiMe3-terminated internal alkynyl alcohols reveals interesting product profiles which include the desired exocyclic ether, a SiMe3-eliminated exocyclic ether, and the SiMe 3-O-functionalized substrate. The rate law for alkynyl alcohol hydroalkoxylation/cyclization is first-order in [catalyst] and zero-order in [alkynyl alcohol], as observed in the intramolecular hydroamination/cyclization of aminoalkenes, aminoalkynes, and aminoallenes. An ROH/ROD kinetic isotope effect of 0.95(0.03) is observed for hydroalkoxylation/cyclization. These mechanistic data implicate turnover-limiting insertion of C-C unsaturation into the Ln-O bond, involving a highly organized transition state, with subsequent, rapid Ln-C protonolysis.;For tandem double intramolecular hydroalkoxylation/cyclization, conversions are highly selective with products distinctly different from those generally produced by conventional transition metal or other catalysts, and the turnover frequencies with some substrates are too large to determine accurately. The rates of terminal alkynl alcohol hydroalkoxylation/cyclization are significantly more rapid than those of internal alkynyl alcohols, arguing that steric demands dominate the cyclization transition state. The hydroalkoxylation/cyclizations of internal dialkynyl dialcohols afford excellent E-selectivity. The rate law for dialkynyl dialcohol hydroalkoxylation/cyclization is first-order in [catalyst] and zero-order in [alkynyl alcohol], as is observed for the organolanthanide-catalyzed hydroamination/cyclization of aminoalkenes, aminoalkynes, and aminoallenes, and the intramolecular single-step hydroalkoxylation/cyclization of alkynyl alcohols. An ROH/ROD kinetic isotope effect of 0.82(0.02) is observed for the tandem double hydroalkoxylation/cyclization. These mechanistic data implicate turnover-limiting insertion of C-C unsaturation into the Ln-O bond, involving a highly organized transition state, with subsequent, rapid Ln-C protonolysis.;Homoleptic lanthanide amido complexes, Ln[N(SiMe3)2] 3 (Ln = La, Sm, and Y) can also do efficiently catalytic amidation of aldehydes with amines. Amidation reactivity follows the trend: La > Sm ≈ Y. These reactions proceed in high yield without added oxidants, bases, and/or heat or light, which are usually required in other catalytic amidation processes. The reaction is demonstrated with a variety of amines, with yields as high as 98% based on amine. |
