Imidazol-5-ones as a substrate for [1,5]-hydride shift triggered cyclization

Abstract

(2-Aminobenzylidene)-imidazolones were used as substrates for [1,5]-hydride shift triggered cyclization under promotion by TiCl4 at room temperature.

Chemodivergent Spirocyclization of 2‐Sec‐Aminobenzilidene Imidazolones: Lewis Versus Brønsted Acids Catalysis

“…In this regard, the hydride shift on the N-methyl derivatives does not occur. As we proved previously, [9] the last stage of the processcyclization of A into 5/5' -is reversible. In this article, we also confirmed this reversibility using compounds 2'd and 5'e.…”

“…Structures of the obtained compounds 2a , 2 a’ and 3a were established by NMR. Determination of the stereochemistry of the diastereomers 2a and 2 a’ was made by comparison of the spectral data with previously obtained compounds from tert‐ amino series, [9] for which the configuration was unambiguously established by X‐Ray analysis. Thus, cis‐ configuration of the major diastereomer 2 a was determined.…”

“…[6] The most commonly known example of such process is "tert-amino effect reaction": [1,5]-hydride shift from α-position of dialkylaniline occurs onto Michael acceptor in ortho-position, followed by cyclization into tetrahydroquinoline (Sche-me 1b, R ¼ 6 H). [7] So far tremendous progress in this field was achieved in recent decades, allowing extension to different [1,n]-shifts, [5,8] various hydride donors and acceptors, [5][6][7]9,10] as well as involvement in multiple cascade and tandem processes. [11] Moreover, not only cyclizations but also various intermolecular reactions triggered by intramolecular hydride shift have been developed.…”

The Cascade [1,5]-Hydride Shift/Intramolecular C(sp3)–H Activation: A Powerful Approach to the Construction of Spiro-Tetrahydroquinoline Skeleton

“…Very recently, Smirnov’s group reported an intramolecular tandem [1,5]-hydride shift and cyclization to form spirocyclic tetrahydroquinoline derivatives 107 under the promotion of TiCl 4 ( Scheme 11B ) ( Zaitseva et al, 2021 ). The hydride shift process was triggered by reactive α,β-unsaturated imidazole fragments 105 .…”

1,5-Hydride-Shift-Triggered Cyclization for the Synthesis of Unsymmetric Julolidines

“…[9][10][11][12][13][14] Such reactions allow tetrahydroquinoline derivatives to be obtained in a straightforward and redox-neutral manner (Scheme 1, previous work). 15 Significant progress in this area is associated with Lewis acid (LA) catalysis, 12,15 especially with the enantioselective procedure developed by Seidel's group, 16 which has allowed various applications involving alternative hydride acceptors [17][18][19][20][21][22][23][24][25] as well as the use of donating groups with shorter or longer tethers. [26][27][28][29][30] Assembly of julolidines via a 1,5-hydride-shift-triggered cyclization could be of benefit due to the unambiguous regioselectivity of hydride transfer and the straightforward access to unsymmetrically substituted derivatives 1 (Scheme 1, this work).…”