N-Boc-protected alkynylamines are converted into the corresponding alkylidene 2-oxazolidinones or 2-oxazinones under very mild reaction conditions in the presence of 1-5 mol % of a cationic Au(I) complex. The scope of the reaction is very general, providing the cyclic carbamates in high yield regardless of the substitution at nitrogen and alkyne terminus.

Dedicated to Professor Josep M. Ribó on the occasion of his 70th birthdayThe 1,3-dipolar cycloaddition of azomethine ylides with alkenes is one of the most powerful and convergent methods for the stereoselective synthesis of pyrrolidines, [1] a heterocyclic moiety widely present in the structure of natural products, pharmaceuticals [2] and chiral ligands. [3] Improving the overall chemical and stereochemical efficiency of this reaction, pioneered by Grigg with stoichiometric metal chiral complexes, [4] a great effort has been devoted in recent years in the development of catalytic asymmetric protocols. In this field a wide variety of outstanding chiral complex catalysts have been reported, [5] mainly Ag I , [5f,g,j,m,q-s] Cu I[5e,h,i,k,l,o,t-w] and Cu II[5d] catalysts, but also Zn II , [5x] Ni II[5n] and Ca II[5p] complexes. In addition, several organocatalytic asymmetric methods have been also developed in the last few years. [6] Concerning the scope of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides, although there is an ample tolerance with regard to the nature of the dipolarophile (i.e., a,b-unsaturated esters, maleimides, a,b-unsaturated nitriles, enones, enals, nitroalkenes, vinyl sulfones and fullerene), the structural variety at the azomethine dipole is much more limited. By far most catalytic asymmetric versions reported to date are based on the use of a-iminocarbonyl substrates, specifically a-iminoesters. The great effectiveness of a-iminoesters as dipole precursors relies on the enhanced acidity of the a-position and the formation of a robust five-membered, N,O-bidentate-metalated, azomethine ylide, which facilitates the asymmetric induction from the chiral ligand. The inherent limitation of this strategy is the restricted structural versatility with regard to the substitution at C2, always providing pyrrolidines with a C2 carboxylate ester substitution.To access other types of substituted pyrrolidines, a-iminonitrile precursors are very appealing, since in the resulting 2-cyanopyrrolidines [7] the cyano group could further act as leaving group allowing its formal substitution by hydrogen or by a carbon nucleophile, [8] and thus leading to a wider variety of substituted pyrrolidines. Two decades ago Kane-A C H T U N G T R E N N U N G masa, Tsuge et al. reported the non-enantioselective thermal [9] and LDA-promoted (LDA = lithium diisopropyl- A C H T U N G T R E N N U N G amide)[10] cycloaddition of alkyl-substituted a-iminonitriles with electron-deficient dipolarophiles, but the catalytic asymmetric version of this process remained to be developed. We describe herein the first catalytic asymmetric procedure for the 1,3-dipolar cycloaddition of a-iminonitriles, as well as some synthetic applications and a DFT theoretical study on the presumed nature of the metalated 1,3-dipole.To evaluate the viability of a-iminonitriles as dipole precursors in catalytic asymmetric 1,3-dipolar cycloadditions, we first studied the reaction of N-benzylidenaminoacetonitrile (1) with meth...

One by one or two by two: In a general approach to the iterative construction of oligopyrroles, the cycloaddition of azomethine ylides derived from pyrrolyl α‐iminoesters with 1,2‐bis(phenylsulfonyl)ethylene is followed by the elimination of the sulfonyl groups in situ under basic conditions. This strategy is amenable to the introduction of one or two pyrrole units in each iterative cycle.

A procedure for the synthesis of functionalized, substituted pyrroles by 1,3-dipolar cycloaddition of azomethine ylides has been developed. This protocol is based on the metal-catalyzed cycloaddition of alpha-iminoesters with sulfonyl dipolarophiles, followed by the base-promoted elimination of the sulfonyl groups. A wide variety of 2,5-disubstituted and 2,3,5- and 2,4,5-trisubstituted pyrroles have been prepared in satisfactory yields from 1,2-bis(sulfonyl ethylene), beta-sulfonylenones, and beta-sulfonylacrylates. This method can be applied in an iterative and straightforward manner to the construction of oligopyrroles, from bipyrroles to pentapyrroles. Iterative [n+1] and [n+2] approaches have been devised, the latter involves double 1,3-dipolar cycloaddition from pyrrolyl-based bis(iminoesters).

A catalytic asymmetric procedure for the 1,3-dipolar cycloaddition of (E)-beta-phenylsulfonyl enones with azomethine ylides to provide highly functionalized pyrrolidine derivatives is described. In the presence of chiral Cu(I)-Segphos catalysts the adducts were obtained with high regio-, diastereo-, and enantioselectivity. Interestingly, a switch from endo to exo selectivity was observed when Segphos or DTBM-Segphos ligand was used.

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Oxazole derivatives R 0220Gold-Catalyzed Synthesis of Alkylidene 2-Oxazolidinones and 1,3-Oxazin-2-ones.-This highly efficient synthesis of two synthetically important structural motifs tolerates a wide variety of substituents both at the nitrogen atom and at the alkyne terminus. In the cyclization of free alcohol (V), MeOH is added in order to avoid trapping of the hydroxyl group by isobutene generated during the reaction. -(ROBLES-MACHIN, R.; ADRIO*, J.; CARRETERO*, J. C.; J. Org. Chem. 71 (2006) 13, 5023-5026; Dep. Quim. Org., Fac. Cienc., Univ. Auton., Cantoblanco, E-28049 Madrid, Spain; Eng.) -Nuesgen 45-124

Pyrrole derivatives R 0120Oligopyrrole Synthesis by 1,3-Dipolar Cycloaddition of Azomethine Ylides with Bissulfonyl Ethylenes. -A one-pot 1,3-dipolar cycloaddition of 1,2-bis(phenylsulfonyl)ethylene with α-iminoesters, followed by in situ aromatization of the adduct through double elimination of the sulfone moieties under basic conditions affords 2,5-disubstituted pyrroles. Through the straightforward conversion of the ester moiety of the pyrrole unit into a new α-iminoester functionality, this procedure can be applied to the synthesis of oligopyrroles and related oligoheterocycles. -(LOPEZ-PEREZ, A.; ROBLES-MACHIN, R.; ADRIO, J.; CARRETERO*, J. C.; Angew. Chem., Int. Ed. 46 (2007) 48, 9261-9264; Dep. Quim. Org., Fac. Cienc., Univ. Auton., Cantoblanco, E-28049 Madrid, Spain; Eng.) -Bartels 15-113