Highly Site Selective Formal [5+2] and [4+2] Annulations of Isoxazoles with Heterosubstituted Alkynes by Platinum Catalysis: Rapid Access to Functionalized 1,3‐Oxazepines and 2,5‐Dihydropyridines

Abstract

Platinum-catalyzed formal [5+2] and [4+2] annulations of isoxazoles with heterosubstituted alkynes enabled the atom-economical synthesis of valuable 1,3-oxazepines and 2,5dihydropyridines, respectively. Importantly, this Pt catalysis not only led to unique reactivity dramatically divergent from that observed under Au catalysis, but also proceeded via unprecedented a-imino platinum carbene intermediates.

Gold-catalyzed intermolecular reaction of ynamides with 3-indolyl azides via an unexpected 1,2-alkyl migration

“…Recently, the generation of a-imino gold carbenes [14][15][16][17][18][19][20][21][22] through gold-catalyzed alkyne amination has gained significant attention, because this strategy offers easy access to a variety of valuable complex nitrogen-containing molecules [23][24][25][26][27][28][29][30][31][32][33]. In our recent study on the ynamide chemistry [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48], we first disclosed that benzyl azides could serve as efficient nitrene transfer reagents to react with ynamides for the intermolecular generation of aimino gold carbenes. As a result, this chemistry has evolved into a robust and reliable method for the construction of versatile 2aminoindoles and 3-amino-b-carbolines (Scheme 2a) [49].…”

Yttrium‐Catalyzed Intramolecular Hydroalkoxylation/Claisen Rearrangement Sequence: Efficient Synthesis of Medium‐Sized Lactams

“…In addition, many 9to 11-membered medium rings can also be synthesized in 52-97 %y ields (entries [3][4][5][6][7][8][9]. Interestingly,t his chemistry could also be extended to the preparation of the macrocycles 4j-l in 58-74 %y ields (entries [10][11][12]. Of note,l ow concentrations are necessary to circumvent the competing intermolecular reaction in the case of the substrates 3k and 3l,a nd as mall amount of the 38-membered ring 4l' ' was detected in the latter case (entry 12).…”

“…[8a] In 2015, Toste et al disclosed its enantioselective version by asymmetric desymmetrization strategy (Scheme 1c). [8b] Despite these remarkable achievements,these intramolecular cascade reactions have so far been limited to noble-metal catalysts.In addition, the construction of important medium-sized rings by this strategy has not been reported to date.I nspired by our recent study on ynamide chemistry, [10,11] we envisioned that the synthesis of eight-membered benzolactams (2)m ight be achieved by catalytic intramolecular hydroalkoxylation of ynamides (1)and subsequent Claisen rearrangement. Herein, we describe the realization of such an yttrium-catalyzed tandem intramolecular hydroalkoxylation/Claisen rearrangement, thus allowing the atom-economical synthesis of various synthetically useful benzazocinones (Scheme 1d).…”

“…When R 2 was either as tyryl or alkyl group,t he desired product, 2i or 2j,r espectively,w as also formed in corresponding yields of 81 and 87 %yield (entries 9and 10). Then, various aryl-substituted ynamides were screened and the reaction furnished the desired 2k-q in 82-99 %y ields (entries [11][12][13][14][15][16][17]. Ther eaction was also extended to other R 1substituted ynamides,a llowing the assembly of the corre- 3 PhCl, 80 8 8C, 2h 78 5 7Y b(OTf) 3 PhCl, 80 8 8C, 2h 88 < 2 8Y (OTf) 3 PhCl, 80 8…”

Ring Expansion and 1,2‐Migration Cascade of Benzisoxazoles with Ynamides: Experimental and Theoretical Studies

“…Ye, [8] Hashmi, [9] and Liu [10] groups independently reported the annulation of Au-carbene species, obtained in situ from ynamides [11] and anthranils or isoxazoles in presence of Au I -catalyst, to provide substituted pyrrole and indole derivatives. By contrast, the generation of a,a'-disubstituted Au-carbenes from ynamides could also be envisaged with the assistance of a1 ,2-di-heteroatom species that would undergo an internal cleavage of the Y-Xb ond (Scheme 1b).…”