Kinetically Controllable Pd-Catalyzed Decarboxylation Enabled [5 + 2] and [3 + 2] Cycloaddition toward Carbocycles Featuring Quaternary Carbons

Abstract

A decarboxylative protocol has been developed toward a range of carbocycles. The key success is based on the use of a batch of newly designed cyclic carbonates as substrates that can provide carbon–carbon zwitterion intermediate under palladium catalysis. The kinetics of the reactions are controllable toward either strained seven- or thermodynamically more favored five-membered carbocycles. The release of this chemistry will shed light on the synthesis of complex and valuable cyclic structures.

Recent Advances in Decarboxylative Conversions of Cyclic Carbonates and Beyond

“…carbocycles (Scheme 14a). 21 In the presence of Pd(PPh3)4 as a pre-catalyst, the kinetics of the reactions could be well controlled under different reaction conditions resulting in either fivemembered cyclopentanones or seven-membered cycloheptenones. Significant solvent effect was observed in these transformations.…”

“…For example, we recently reported the synthesis and Pd-catalytic decarboxylation of vinyl methylene cyclic carbonates (VMCCs). 21 In the presence of a palladium catalyst, the cyclic carbonate A may undergo decarboxylation to generate the zwitterionic enolate intermediate T1 or the corresponding six-membered palladacycle tautomers T2 or T3 ; under high reaction temperatures, the generation of vinyl Pd-oxyallyl T4 is also feasible (Scheme 13 ). The capture of these reactive intermediates T1 – T4 with suitable electrophiles or nucleophiles proved to be feasible, affording various highly functionalized (cyclic)ketones which are otherwise synthetically quite challenging.…”

“…For instance, in the presence of a Pd catalyst, the decarboxylative cyclization of VMCC A and benzylidene malononitrile could be accomplished toward the formation of carbocycles (Scheme 14a ). 21 In the presence of Pd(PPh 3 ) 4 as a pre-catalyst, the kinetics of the reactions could be well controlled under different reaction conditions, resulting in either five-membered cyclopentanones or seven-membered cycloheptenones. A significant solvent effect was observed in these transformations.…”

“…In contrast, we observed that the five-membered products could be formed smoothly without the addition of any ligands at room temperature. 21 However, the reaction toward the formation of Ir PC (1.0 mol%)…”

A Dipolar Cyclization/Fragmentation Strategy for the Catalytic Asymmetric Synthesis of Chiral Eight-Membered Lactams

“…[8][9][10][11][12][13][14][15][16][17][18][19][20] In particular, recent studies have proven that Pd-catalyzed asymmetric processes involving π-allyl-Pd-type dipoles can produce a variety of medium-sized chiral heterocycles. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Mechanistically, in situ generated MSRDs (M = Pd) usually react with electrophilic dipolephiles to generate prolonged dipolar species; subsequently, intramolecular direct head-to-tail cyclizations produce the desired heterocycles (Figure 1, up). Despite impressive advances, this strategy has intrinsic limitations involving the competitive self-cyclization of MSRDs and the oligomerization of the prolonged dipolar species due to unfavorable entropy and enthalpy effects.…”