Silyl Assistance in the Intramolecular Addition of Pyridyl Radicals onto Pyridines and Quinolines

Abstract

Abstract:The first example of a stable acylazinium salt obtained by an intramolecular acylpyridine-centered radical attack on azine nitrogen atoms is reported. Depending on the relative position of the bromo substituent on the attacking amino-

Thirty Years of (TMS)3SiH: A Milestone in Radical-Based Synthetic Chemistry

“…Supported by DFT calculations, Beckwith-Dowd radical ring expansion was invoked to rationalize the puzzling cyclization of closely related bromopyridines 357a−357b, which led to the quinazolinium bromide 358a and quinolone 358b, respectively, after ipsoaddition of the aryl radical onto the quinoline ring and rearrangement through intermediates III and IV. 258 The cyclobutylmethyl radical is known to fragment easily (k = 5 × 10 3 s −1 ), although at a slower rate than the corresponding cyclopropyl analogue (k = 6.7 × 10 7 s −1 ). 259 An interesting example of such rearrangement is provided with the quantitative TTMSS-ring expansion of 359 into the seven-membered ring 360.…”

“…Lactones spirofused to larger cycloalkanones such as 356 were also accessible from ketoester 355 , using this strategy. Supported by DFT calculations, Beckwith-Dowd radical ring expansion was invoked to rationalize the puzzling cyclization of closely related bromopyridines 357a – 357b , which led to the quinazolinium bromide 358a and quinolone 358b , respectively, after ipso -addition of the aryl radical onto the quinoline ring and rearrangement through intermediates III and IV …”

Studies on the preparation of aminobipyridines and bipyridine sultams via an intramolecular free radical pathway

“…The experimental evidence points to a trend in the reactivity depending on whether the Br substituent is positioned on either C2 0 (3aa and 3ab) or C3 0 (3ba and 3bb) of the attacking pyridine. 16 Scheme 4 Proposed in situ deprotonation of pyridine sulfonamide 8d to give the double sulfonylation product 9. Thus, those substrates with a Br in the C2 0 position of the pyridine (3aa and 3ab) yield the C4-substituted derivatives as the main products (5aa and 5ab, respectively, Scheme 8) due to the repulsion generated by the proximity of the radical to the non-binding pairs of both nitrogens in the adduct intermediate.…”

Planar Blatter radicals through Bu3SnH- and TMS3SiH-assisted cyclization of aryl iodides: azaphilic radical addition

“…38,39,45–48 In all these reactions, the key step is the attack of the transient C-centered radical onto the ring C-atom, which is preferred over the N-attack, if the two paths are available. 49,50 Consequently, N-attack of an aryl radical has never been observed in tin- or silicon-hydride-assisted radical cyclization processes.…”