New Applications ofN-Acyliminium Precursors: Tetracarbonyliron-Mediated Stereoselective Alkylations of 5-(R)-Isopropoxy-3-pyrrolin-2-ones

Abstract

Lewis acid catalyzed allylic substitutions with several nucleophiles at C‐5 of the cis‐tetracarbonyliron complexes of N‐acetyl‐ and N‐tosyl‐5‐(R)‐isopropoxy‐3‐pyrrolin‐2‐ones occur highly regio‐ and stereoselectively. The results are interpreted as being indicative of the intermediacy of a (π‐allyl)tetracarbonyliron cation, with possible preceding formation of an N‐acyl‐ or an N‐tosyliminium ion.

Improved Synthesis ofC2-Symmetrical Pyridinediols and Synthesis ofCs-Symmetrical Pyridinediols

“…In the past, we have developed a synthetic approach to chiral non-racemic pyridine thiols and dithiols, [3] and have, for example, applied the thioethers thereof in palladium-catalyzed allylic substitution. [4] Sterically bulky C 2 -symmetrical pyridine diol ligands like 3 obtained by condensation of ketones with lutidine 1 are of special interest as complexing agents for the development of new homogeneous catalysts. The combination of two hydroxy groups and the pyridine nitrogen atom leads to ligands capable, for example, of stabilizing high-valent osmium alkoxide complexes.…”

“…: 2,6-Lutidine (1) (1.0 g, 0.9 mmol) in 50 mL of THF was lithiated with n-butyllithium (1.6  in hexane, 6.2 mL, 9.9 mmol) at Ϫ60°C. After stirring for 10 min (R)-(Ϫ)fenchone (1.4 g, 9.2 mmol) in 5 mL of THF was added and stirring was continued for 1 h. NH 4 Cl was added and the mixture was extracted with ethyl acetate yielding 2f as a mixture of the exo and endo isomers (1.9 g, 7.3 mmol, 79%).…”