A Kulinkovich Entry into Tertiary N-Acyliminium Ion Chemistry

Abstract

Subjection of N-alkenylimides to Kulinkovich cyclopropanation conditions led to different types of N,O-acetals, which were used as precursors for tertiary N-acyliminium ion chemistry. In this way, a variety of bi- and tricyclic lactams were efficiently synthesized.

Creation of quaternary stereocentres: synthesis of new polyhydroxylated indolizidines

“…Bijvoet-pair analysis as implemented within PLATON (Spek, 2003), 23b performed on the dataset using the copper radiation, supports the selected relative stereochemistry of the asymmetric carbons, namely 6R,7S, and 8aR. C 15 …”

“…[13][14][15] Starting from 2, we developed a new and simple access, in one step, to bicyclic 5-hydroxylactam 7, which acts as a precursor to a trisubstituted acyliminium ion (Scheme 2). 9,12 The formation of 7 was the result of a double protonation at C-7 and C-6, followed by trapping the N-acyliminium ion thus obtained by the nucleophile.…”

Synthetic Chemistry with N-Acyliminium Ions Derived from Piperazine-2,5-Diones and Related Compounds

“…Addition of organolithium or Grignard reagents to N-alcoxycarbonyl-DKPs leads to tertiary hydroxylactam derivatives 15, less stable than the above mentioned secondary reduction products 14 [46]. These hemiaminals, that may be obtained by alternative procedures (see Section 5), often exist as mixtures of cyclic and linear tautomers 16 and usually give N-acyliminium species of type 8 under acid catalysis (Scheme 2) [47][48][49].…”

Bis alkoxytitanacyclopropanes and -propenes (Kulinkovich reagents): Versatile reagents for carbon—carbon bond formation

“…Additionally, these bicyclic aminals can be functionalized further, since they serve as ideal precursors to entry immonium-type chemistry [12].…”

“…Hydrolysis of the titanium-carbon bond furnished the half-aminal 34. (12) add to the ester-carbonyl to give cyclopentadienols 39 which are of interest as synthetic intermediates since they allow further functionalization of up to five carbon atoms. Remarkably, primary iodides are tolerated under these reaction conditions.…”