The 1,2-migration of tetracoordinated boron compounds represents a powerful strategy for the construction of C–C bonds and stereogenic centers, enabling the efficient synthesis of complex organic molecules under mild conditions. In recent years, substantial progress has been made in this field through the 1,2-migration of alkynylboronates, affording a diverse array of alkenylboron and allylic boron derivatives. In this context, electrophilic reagents readily induce the 1,2-migration of alkynylboronates, while high-oxidation-state π-acidic late transition metals, such as Pd2+ and Ni2+, have also proven effective as catalysts in reactions involving alkynylboronates. This review systematically summarizes the advances in 1,2- and 1,3-migration processes of alkynylboronates, as well as transformations involving three-component coupling reactions. Key developments include the reactions of alkynylboronates with a variety of electrophiles (protons, halogens, sulfurs, and iodonium species, et al.) to access tetrasubstituted alkenes, alkenyl halides, benzothiophenes, boracycles, and allylamines; the development of cascade and one-pot strategies that streamline synthetic routes from simple alkynes; and the integration of asymmetric catalysis for the stereoselective construction of carbon stereocenters and axial chiral motifs. The discussion also extends to the reaction scope, mechanistic studies, and synthetic utility of the methodologies described herein.
Sulfur-sulfur bond activation by a stable phosphinyl radical was investigated. Treatment of the radical with di-p-tolyl disulfide afforded a p-tolylthiophosphine via an SH2 process followed by radical coupling. Reaction of the phosphinyl radical with S8 selectively provided a 1,6-bis(thiophosphoryl)hexasulfide as the initial product.The formation of the hexasulfide suggests that both radical and nucleophilic S-S bond activation processes drive this reaction. The hexasulfide gradually decomposed into phosphorus-sulfur heterocycles such as 2,3-thiaphosphirane 1-sulfide, dithiaphosphetane 1-sulfide, and 2,3,4-trithiaphospholane 1-sulfide.Based on the structures of products, silyl migration from carbon to sulfur atoms is proposed as the key step in the formation of the phosphorus-sulfur heterocycles.
Abstract 1,2-Di-ω-(pyren-1-yl)alkanoyl-sn-glycero-3-phosphocholines with C4, C6, C8, and C10 alkanoyl chain lengths, which are useful fluorescent probes for sensing changes in the physical properties of amphiphilic membranes such as fluidity or lateral pressure, were prepared in —two to three steps from 5-(pyren-1-yl)-1-pentene as a common precursor. This pyrenylpentene was generated from 1-bromopyrene by halogen–metal exchange (n-BuLi, TMEDA, THF, 0 °C) followed by alkylation of the aryllithium with 5-bromo-1-pentene (66% yield). The C4 lipid target was uniquely prepared by oxidative cleavage of the pyrenylpentene intermediate (cat. OsO4, Oxone, DMF, rt; 53% yield) followed by diacylation of sn-glycero-3-phosphocholine with the resulting 4-(pyren-1-yl)butanoic acid (CDI, CH2Cl2, rt; DBU, DMSO, 40 °C; 50% yield). The C6, C8, and C10 lipid targets were accessed by conversion of 5-(pyren-1-yl)-1-pentene to the appropriate chain-length ω-(pyren-1-yl)alkanoic acid (C6: 72% yield; C8: 72% yield; C10: 77% yield), by olefin cross-metathesis (with Grubbs 2 catalyst, CH2Cl2, 40 °C) with acrylic acid, 4-pentenoic acid, or 6-heptenoic acid, respectively, followed by hydrogenation (H2, Pd/C, EtOAc-EtOH); and then, diacylation of sn-glycero-3-phosphocholine with the pyrenyl alkanoic acid using the above CDI-based method (C6: 43% yield; C8: 39% yield; C10: 59% yield). In all cases, potentially useful 1-ω-(pyren-1-yl)alkanoyl-sn-glycero-3-phosphocholines were obtained as minor products from the esterification process (21–36% yield).
A mild and practical approach to the formation of benzylic fluorides is reported via an AgBF4 -catalyzed oxidative fragmentation of acyclic homobenzylic alcohols. Following β-scission and extrusion of acetone, experimental evidence suggests that the reaction proceeds via the generation of a benzylic radical intermediate capable of reaction with Selectfluor, which acts both as fluorinating agent and oxidant for the Ag(I) catalyst. The method is amenable to the production of various fluoromethylated aromatic systems typically sensitive to oxidation such as polycyclic or electron-rich arenes.
Isocyanide multicomponent reactions such as the Ugi fourcenter reaction are attractive for DNA-encoded library design because they allow for synthesizing diverse peptidomimetic and heterocyclic scaffolds from large numbers of simple and readily available starting materials. DNA amino acid conjugates with free N-terminus were solubilized in dry organic solvents with the help of an amphiphilic polyacrylate copolymer additive. This recently developed method allowed for reacting the DNA-tagged substrates with carbaldehydesubstituted arylcarboxylic acids via high-yielding and robust Ugi fourcenter three-component reaction to lactams and with cyclic ketones via Ugi four-center four-component reaction to diverse substituted peptidomimetic compounds that contain a central heterocyclic scaffold.Herein we discuss the scope and limitations of these two isocyanide multicomponent reaction strategies for DNA-encoded library synthesis.
