.alpha.-Keto dianions. New reactive intermediates

Thermochemical Considerations of Metal Enolates

“…For example, no 5-methyl-2-furanol (41) is detected in the rearrangement of γ -methylene-γ -butyrolactone (42) to α-angelicalactone (43) 228 . Understanding the contribution to aromaticity of Re in the 2-rhenafurans (39,40) and the exocyclic and endocyclic methylene groups in 42 and 43 would be most instructive. acidities of the diverse sites for deprotonation is welcomed.…”

Lithium synthetic reagents: dimerization and intramolecular association. Double bridging in "dianions"

“…Thus, ketones can be dimetallated: "1,3-dianions" have been known for some time (la,18), and "l,l-dianions" prepared more recently (19). Carboxamides, RCONH9, can also be metallated twice (la).…”

Metal-Catalyzed Synthesis and Transformations of β-Haloenol Esters

“…In this context, while the utility of α-haloenol esters remains almost unexplored due to the lack of efficient and general synthetic methods [7][8][9][10], more accessible β-haloenol esters have gained significance in recent years as coupling partners in diverse chemical transformations. Several methodologies can be employed for the preparation β-haloenol esters, the most classical ones involving the acylation of haloenolate anions [11][12][13][14][15] or the haloacyloxylation of alkynes employing the elemental halogens [16][17][18][19][20], bis(pyridine)iodonium tetrafluoroborate (IPy2BF4) [21][22][23][24][25], N-halosuccinimides (NXS; X = Cl, Br, I) [26][27][28], PhI(OAc)2 [29][30][31], trihaloisocyanuric acids [32] or N,N-dibromo-p-toluenesulfonamide (TsNBr2) [33] as the electrophilic halogen source (Scheme 1). In this context, while the utility of α-haloenol esters remains almost unexplored due to the lack of efficient and general synthetic methods [7][8][9][10], more accessible β-haloenol esters have gained significance in recent years as coupling partners in diverse chemical transformations.…”

“…In this context, while the utility of α-haloenol esters remains almost unexplored due to the lack of efficient and general synthetic methods [7][8][9][10], more accessible β-haloenol esters have gained significance in recent years as coupling partners in diverse chemical transformations. Several methodologies can be employed for the preparation β-haloenol esters, the most classical ones involving the acylation of haloenolate anions [11][12][13][14][15] or the haloacyloxylation of alkynes employing the elemental halogens [16][17][18][19][20], bis(pyridine)iodonium tetrafluoroborate (IPy 2 BF 4 ) [21][22][23][24][25], Haloenol lactones of type A and B (see Figure 2) are also a relevant class of compounds due to their biological activity as enzymes inhibitors [34][35][36][37][38], and also because they are a common structural motif in many natural products [39]. Access to these molecules is usually achieved by halolactonization of the corresponding alkynoic acid using I2, NBS, NIS or related halogenating agents, reactions that deliver the haloenol lactone products as the E isomers exclusively (Scheme 2) [34][35][36][37][38]40,41].…”