Organometallic enantiomeric scaffolding: general access to 2-substituted oxa- and azabicyclo[3.2.1]octenes via a Brønsted acid catalyzed [5 + 2] cycloaddition reaction.

6-Substituted TpMo(CO) 2(eta-2,3,4-pyranyl)- and TpMo(CO) 2(eta-2,3,4-pyridinyl) scaffolds (Tp = hydridotrispyrazolylborato) function as reaction partners in an efficient regio- and stereocontrolled synthesis of functionalized oxa- and azabicyclo[3.2.1]octenes through a novel Brønsted acid catalyzed [5 + 2] cycloaddition reaction. Excellent exo-selectivities are obtained, and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, nonracemic scaffolds. The substituent at C-6 of the eta (3)-coordinated heterocyclic scaffold not only influences [5 + 2] reactivity but also plays a critical role in the demetalation step directing the reaction to only one of two possible products.

Highly diastereoselective synthesis of C6-functionalized dihydroimidazotriazines.

[reaction: see text] The first examples of C(6)-substituted 7-hydroxy-6,7-dihydro-5H-imidazo[1,2-b][1,2,4]triazines have been prepared by ring closure of different 5(2H)-1,2,4-triazin-3-ones 1a-c with 40% aqueous glyoxal and various nucleophiles (alcohols, thiols, or amines). The structure and exact stereochemistry of 2a was established by a single X-ray diffraction study and (1)H and (13)C NMR spectra analysis. The process was shown to be totally regio- and diastereoselective. A mechanism involving an imine intermediate was proposed.

Easy access to 3- or 5-heteroarylamino-1,2,4-triazines by S(N)Ar, S(N)H, and palladium-catalyzed N-heteroarylations.

In this paper, N-arylations between two heteroaryl compounds were studied. Conditions were found to generate selectively either 3- or 5-heteroarylamino-1,2,4-triazines by investigating anionic processes (use of bases such as 2,2',6,6'-tetramethylpiperidine/tBuOK/nBuLi) or Pd-catalyzed N-arylations [Pd(OAc)(2), xantphos]. These methods were successfully applied to a wide variety of heteroarylamines and allowed us to pursue our work on fused polynitrogen compounds synthesis.