Engaging 1,7-diynes in a photocatalytic Kharasch-type addition/1,5-(S_N′′)-substitution cascade toward β-gem-dihalovinyl carbonyls

Abstract

A new and general photocatalytic Kharasch-type addition/1,5-(SN′′)-substitution cascade of 1,7-diynes with alkyl halides such as BrCCl3 and CBr4 was reported for the first time, producing 65 hitherto unreported β-gem-dihalovinyl ketones/aldehydes with moderate to excellent yields.

Photocatalytic Biheterocyclization of 1,7-Diynes for Accessing Skeletally Diverse Tricyclic 2-Pyranones

“…Combined with these observations and a literature survey, ,, a reasonable reaction pathway for products 3 is illustrated in Scheme . First, upon exposure to visible light, the excited state of *Ir­(III) complex is rapidly formed from a normal Ir­(III) complex.…”

“…Moreover, radical-triggered 1, n -diyne cyclizations have emerged as a powerful platform for assembling multiple functionalized ring structures of chemical and pharmaceutical interest . Very recently, our group disclosed a general and practical photocatalytic Kharasch addition/S N ″-substitution cascade of secondary alcohol-linked 1,7-diynes, resulting in functionalized β-naphthyl ketones. As the continuation in our development of new photocatalysis approaches, we questioned whether the reaction can be directed toward photocatalytic benzannulation to generate heterocyclic ketones when secondary alcohol-linked 1,7-diynes are replaced by heteroatom-linked 1,7-diynes as radical acceptors.…”

“…Subsequent 1,5-(S N ″)-substitution between D and OH – from H 2 O in the presence of the base gives intermediate E (detected by LC-MS, MS = 409.9), which loses one molecule of HBr to render intermediate F (detected by LC-MS, MS = 330.0) via an elimination reaction. Different to the conversion of secondary alcohol-linked 1,7-diynes, the in situ -generated intermediate F from heteroatom-linked 1,7-diynes has a larger conjugated system with a strong electron-donating nature, which easily undergoes 6π-electrocyclization under visible light irradiation to yield intermediate G . Finally, double nucleophilic substitutions between G and OH – occur, affording pyrano­[3,4- c ]­chromen-2-one 3a through the dehydration.…”

Visible-Light-Driven Photocatalytic Kharasch-Type Addition of 1,6-Enynes

“…在过去的几十年里, 大量的 开创性工作证明了光催化反应在有机合成中的巨大潜 力 [14] . 最近, 我们课题组利用可见光催化策略实现了 1,7-二炔与多卤代烃的 Kharasch 加成和 1,5-亲核取代串 联反应 [15] . 该反应过程无需氧化剂, 为 β-gem-二卤烯基 酮的合成提供一种绿色有效的合成方法, 但此反应中底 物的原子利用率不能令人满意.…”

Nitrative bicyclization of 1,7-diynes for accessing skeletally diverse tricyclic pyrroles

“…Very recently, we elaborated a photocatalytic Kharasch-type addition-based bicyclization cascade of available heteroatom-linked 1,7-diynes with trichlorobromomethane and H 2 O, delivering a series of skeletally diverse tricyclic 2-pyranones. 15 Inspired by Li's work 14 and aiming to further expand radical bicyclization of 1, n -diynes, 16 we conceived that NO 2 radicals derived from TBN under thermolytic conditions could add to 1,7-diynes, followed by 6- exo-dig cyclization, radical cross coupling and 5- endo-trig cyclization to produce tricyclic pyrroles. Such a notion would then enable us to achieve TBN with dual roles as a nitro precursor as well as a nitrogen source of the pyrrole ring.…”