4.22 Intermolecular 1,3-Dipolar Cycloadditions of Alkenes, Alkynes, and Allenes

Decarbonylative Formation of Homoallyl Radical Capable of Annulation with N-Arylpropiolamides via Aldehyde Auto-oxidation

“…The possible mechanism for this cascade annulation protocol was proposed on the basis of the previous works − and the present results (Scheme ). Initially, hydrogen-abstraction from aldehyde 2a by O 2 affords the carbonyl radical intermediate A and the • OOH radical. , The carbonyl radical intermediate A is not stable under heating and quickly undergoes decarbonylation to form the homoalkyl radical intermediate B , ,, which sequentially undergoes the addition across the CC bond of alkyne 1a and then annulation with the CC bond to give the intermediate D . , By using N -phenylpropiolamide 1a , the intermediate D executes a sequence of the second annulation with the N -aryl ring and oxidative deprotonation to access the desired product 3aa .…”

“…The cascade annulation reaction to construct various carbo- and heterocylic frameworks is a well-established powerful methodology in synthesis . Despite impressive advances in the field, examples via radical-mediated intermolecular annulation with alkynes , are less abundant, which still confront the aforementioned challenges in the classic technologies.…”

“…The cascade annulation reaction to construct various carbo- and heterocylic frameworks is a well-established powerful methodology in synthesis . Despite impressive advances in the field, examples via radical-mediated intermolecular annulation with alkynes , are less abundant, which still confront the aforementioned challenges in the classic technologies. We here report a new metal-free aliphatic aldehyde auto-oxidative strategy for oxidative decarbonylative formation of homoalkyl radicals, which sequentially undergoes [3 + 2]/[5 + 2] cascade annulation with the N -arylpropiolamides to access ring-fused cyclopentene skeletons (eq 3; Scheme b).…”

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…The versatile and convergent nature of the 1,3-dipolar cycloaddition reaction has led to its development as a powerful method for the synthesis of five-membered heterocycles [1][2][3][4][5][6][7]. The reaction involves the addition of 1,3-dipoles, such as azides, nitrones, carbonyl ylides, nitrile oxides, nitrile imines and azomethine ylides to unsaturated double or triple bonds (1,2-dipolarophiles) [8][9][10][11][12][13][14][15].…”

Electro-alkynylation: Intramolecular Rearrangement of Trialkynylorganoborates for Chemoselective C(sp2)–C(sp) Bond Formation

“…Alkynes are also often used as versatile intermediates in synthesis, constituting reactive moieties in stereoselective hydrogenations, halogenations, (3 + 2)-Huisgen cycloadditions, hydro- and carbometalations, gold-catalyzed rearrangements, and cyclopropenations …”