Ethanol is shown to act as a hydrogenating agent for ynamides under palladium catalysis. This behavior is different from the normally expected reaction of ethanol addition to alkynes. The reaction ...shows stereoselectivity for E enamides, which is in contrast to reports using other hydrogenating sources. The method was also extended to ynamines. Alternatively, the use of ethanol and ammonium formate as the hydrogenating source gives Z enamides. The role of ethanol in hydrogenation was demonstrated by means deuterium labeling experiment.
One for the road: Ethanol acts as a hydrogenating agent for ynamides under palladium catalysis. This behavior is different from the normally expected addition of ethanol to alkynes. The reactions show stereoselectivity for E enamides, which is in contrast to reports using other hydrogenating sources, and the method was also extended to ynamines. Alternatively, the use of ethanol/ammonium formate as the hydrogenating source gives Z enamides.
A novel and efficient Cu-catalyzed one-pot regio- and stereospecific synthesis of benzo1,4,2dithiazine 1,1-dioxides and benzo1,4,2thiaselenazine 1,1-dioxides by cyclization of functionalized ...ynamides with elemental sulfur/selenium has been developed. Its generality is elegantly illustrated by extension to benzodithiazepines and benzothiaselenazepines. Involvement of water in the reaction is demonstrated by the incorporation of 2D at the olefinic site by using D2O in place of water. Selective oxidation at sulfur in benzo1,4,2dithiazine 1,1-dioxide by using mCPBA as the oxidizing agent is also described.
Indole‐substituted purine nucleobases have been synthesized by Ru‐catalyzed oxidative annulation of 6‐anilinopurines with internal alkynes that involves CH activation. Unsymmetrical ...aryl(alkyl)alkynes led to high regioselectivity. The reaction was also successful with nucleosides by delivering unprotected indole‐substituted nucleosides. In the presence of RuCl2(p‐cymene)2 and copper(II) acetate hydrate Cu(OAc)2⋅H2O, in some cases, we have observed two‐fold CH activation products that exhibit fluorescence. A ruthenacycle intermediate was characterized by crystallography, which suggests that the N‐1 nitrogen atom of the purine acts as a directing group for the present transformation.
Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of ...allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and P(III)-Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.
Recent research about Mitsunobo and other reactions is discussed. The Mitsunobu reaction is an important part in the synthesis of many organic transformations.
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•Catalytic semihydrogenation of alkynes is a direct and simple route to alkenes.•Both chemoselectivity and stereoselectivity are critical to obtain desired products.•This digest ...highlights, developments in this area during the past decade.
The chemoselective semihydrogenation of alkynes is one of the most important reactions in synthetic organic chemistry. During the last decade or so, a multitude of innovative catalytic methods have been developed to address the selective hydrogenation of alkynes. This digest focuses on the recent developments in chemoselective semihydrogenation of alkynes to alkenes.
Lewis base dependent (3+3) annulations of β′/δ‐acetoxy allenoates with iminoindolines offer α‐carbolines with varying substituents depending on the base used as well as subtle changes in the reaction ...conditions. The phosphine‐catalyzed annulation of δ‐acetoxy allenoates with iminoindolines involves 6‐exo‐trig cyclization, tosyl anion elimination/trapping, and ethyl acetate elimination as key steps in delivering β‐H and γ‐tosyl containing α‐carbolines. An unobvious elimination (by Cα‐Cβ bond cleavage) of the −CH2CO2Et moiety is observed here. The same reactants under DBU catalysis offer α‐carbolines that retain −CH2CO2Et moiety but are devoid of −Ts group via 6‐exo‐dig cyclization. The reaction of β′‐acetoxy allenoate with iminoindolines is completely tertiary amine dependent; the use of DABCO affords tetrahydro‐α‐carbolines exclusively with excellent stereoselectivity while DBU offers substituted α‐carbolines that are distinct from those using DABCO. Several control experiments and HRMS studies have been done in support of a plausible reaction mechanism.
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•Functionalized oxazoles are prepared using copper catalysis.•Oximes and carbenoid precursors have been utilized.•Two reducible functionalities (esters or ester + cyano) are ...introduced on oxazoles.
An operationally simple, economical and straightforward synthesis of diverse oxazoles from oximes possessing a vicinal carbonyl group has been achieved by treatment of the latter with terminal diazo compounds like ethyl/benzyl diazoacetate and diazoacetophenone (which act as carbenoids) in one pot. At least two reducible functional groups (two ester groups or cyano + ester) are simultaneously introduced in one step. This reaction involves expulsion of a molecule each of N2 and water only as byproducts under copper catalysis. The structure of one of these oxazoles is confirmed by X-ray crystallography. Both the ester groups in the oxazole product could be reduced to alcohol moieties by using NaBH4/EtOH.
A palladium‐catalyzed tandem‐cyclization of functionalized ynamides to afford a wide range of hetero‐substituted benzosultams (1,2‐benzothiazine 1,1‐dioxides) has been achieved. Medicinally useful ...compounds like nortriptyline and eugenol could also be used as nucleophiles. Base has a significant effect in the cyclization process, depending on the nucleophile source used. DFT studies suggest that the reaction involves a Pd(II)–Pd(0)–Pd(II) cycle. Structures of key products were proven by X‐ray crystallography.
In reactions centered at phosphorus, whether chemical or biochemical, a pentacoordinate transition state species or an intermediate or a stable molecule is very often encountered. In this Account, ...recent developments in this important area are discussed and compared with the earlier literature. Particular reference, with results from our laboratory, will be made to the apicophilicity, fluxional behavior, bond parameters, and tetra- vs pentacoordination. It is shown that the familiar apicophilicity rules give an oversimplified picture as demonstrated by several exceptions. Extremities of the P−O or P−N bond distances in PX4N and PO4N systems as revealed by a database search and possible future directions in this area are also discussed.
