Palladium(0)‐Catalyzed Tandem Cyclization of Allenenes

Palladium‐Catalyzed Asymmetric Amination of Allenyl Phosphates: Enantioselective Synthesis of Allenes with an Additional Unsaturated Unit

“…Theuniquereactivityofallenesandtheiroccurrenceinmany natural products, pharmaceuticals, [1] and chiral ligands in asymmetric organic reactions [2] make the enantioselective synthesis of optically active allenes with both axial and/or central chirality a hot topic in chemistry. [3] 2,3-Allenyl amines have been widely used in organic synthesis to construct heterocyclic compounds, [4,5] and efficient, enantioselective approaches to optically active 2,3-allenyl amines are highly desirable. The Pd-catalyzed asymmetric synthesis of axially chiral allenyl amines has been reported for some cases, [6] but a catalytic asymmetric approach to optically active 2,3-allenyl amines with a-central chirality has never been realized.…”

“…Considering the importance of allenes with an additional unsaturated CÀC bond and the nature of the amine, [4,5] 2 a was chosen as the amine substrate for this catalyzed substitution. By conducting the reaction of 2,3-allenol acetate 1 a with 2 a using [Pd(Allyl)Cl] 2 , different ligands ((R)-L1-L5, see Fig-ure S1 in the Supporting Information), and DBU as the base, we observed that (R)-L5 gave the best ee value (86 % ee), although the yield was not satisfactory (Table 1, entry 1).…”

Thermal Intramolecular [2+2] Cycloaddition of Allenenes and Allenynes: Diastereoselective Access to Bicyclic Nitrogen Heterocycles

“…[7] In most reported intramolecular [2+2] cycloaddition reactions of simple unactivated allenes, the proximal 2p component of the allene moiety participates in the cycloaddition to form bicyclic products 2. [12] In the course of our efforts toward the development of a new methodology for the synthesis of heterocyclic compounds by the transition-metal-catalyzed cyclization of allenes, [4,13] we found that the thermal cycloaddition of simple allenes with an additional multiple bond proceeds by simply heating the allenenes or allenynes in the absence of any catalyst. [12] In the course of our efforts toward the development of a new methodology for the synthesis of heterocyclic compounds by the transition-metal-catalyzed cyclization of allenes, [4,13] we found that the thermal cycloaddition of simple allenes with an additional multiple bond proceeds by simply heating the allenenes or allenynes in the absence of any catalyst.…”

“…[1] Considerable research efforts have been particularly focused on the development of cycloaddition of allenes, [2] on account of the current interest in the reactions of allenes with an additional multiple bond, including transitionmetal-catalyzed carbocyclizations. [3,4] The [2+2] cycloaddition reactions [5] between allenes and alkenes are extremely useful for the synthesis of methylenecyclobutane derivatives. [6] Especially, intramolecular cycloaddition constitutes a versatile method for the stereoselective synthesis of a variety of bicyclic compounds having a strained bicyclo[n.2.0] framework (Scheme 1).…”

“…[2] Only limited examples of the intramolecular [2+2] reaction of the distal allenic double bond to give 3 have been reported to date, which used a special class of allenes such as allene carbox-ylates, [8] allenyl sulfones, [9] difluoroallenes, [10] b-lactam-tethered allenes, [11] or diyne-diallenes. [12] In the course of our efforts toward the development of a new methodology for the synthesis of heterocyclic compounds by the transition-metal-catalyzed cyclization of allenes, [4,13] we found that the thermal cycloaddition of simple allenes with an additional multiple bond proceeds by simply heating the allenenes or allenynes in the absence of any catalyst. Herein, we present an intramolecular [2+2] cycloaddition of unactivated allenes to form distal adducts of type 3, which constitute an important class of compounds in synthetic [14] and natural product chemistry.…”