A novel design of a levoglucosenone derived chiral auxiliary

A two-step general approach to a new chiral auxiliary starting from levoglucosenone is reported. The compound is obtained by a [4+2] cycloaddition reaction with anthracene followed by a diastereoselective reduction of the C-2 keto function in high overall yield. The auxiliary has been used as chiral template in an asymmetric Diels-Alder reaction of the corresponding acrylic ester derivative with cyclopentadiene and shown to be efficient for asymmetric induction.     

Synthesis of 2-Acyl-2H-1,2,3-diazaphospholes and Their Diels-Alder Reaction with Cyclopentadiene

2H-1,2,3-Diazaphospholes 3a-3h were prepared from various ketone acylhydrazones and phosphorus trichloride in the presence of triethylamine. Compounds 3 underwent feasible hetero-Diels-Alder reactions with cyclopentadiene to afford the respective anellated [1,2,3]diazaphospholes 4a--4d as well as 4a‘--4d‘ in moderate yields. The endo rule in the reaction was observed under kinetic control conditions.     

Diels-Alder-Reaktionen von Vinylindolen mit Arin und 1,4-Benzochinonen: Neue potentielle DNA-Interkalatoren

Summary Diels-Alder reactions of 2- and 3-vinylindoles with aryne, 1,4-benzo- and 1,4-naphtho-quinone lead to new six-ring annellated carbazoles. Molecular modeling studies predict that the compounds with coplanar framework are able to intercalate with the B-DNA.

     

Synthesis and crystal structures of extremely crowded oligophenylenes as model precursors to ‘cubic graphite’

By using drastic conditions for a Diels-Alder cycloaddition reaction, it was possible to synthesize an oligophenylene with an extremely dense packing of the benzene rings. Crystallographic data could be obtained and a projection of the structure on the plane of the central phenyl ring reveals that the molecule retained its theoretical threefold symmetry with only minor deviations. Due to its dense packing of interlocked benzene rings, this oligophenylene could be furthermore used as a suitable precursor for constructing a subunit of ‘cubic graphite’.     

Strained silacycle-catalyzed asymmetric Diels-Alder cycloadditions: the first highly enantioselective silicon Lewis acid catalyst

The first highly enantioselective silicon Lewis acid catalyst for an asymmetric organic transformation has been developed. The catalyst derives its activity from the strain induced in the silicon center by virtue of being constrained in a five-membered ring. A simple tridentate ligand has been developed and the derived chlorosilane complex catalyzes the Diels-Alder cycloaddition of methacrolein and cyclopentadiene with 94% ee.     

Asymmetric intramolecular Diels-Alder reaction of a sulphoximine-substituted triene

The synthesis and thermally-induced intramolecular Diels-Alder (IMDA) reaction of (S)_s-(+)-S-[(1E,7E)-1,7,9-decatrienyl]-S-phenyl-N-(p-tolylsulphonyl)sulphoximine 4 is described. A model is proposed for the cis-selectivity of the cycloaddition based on previous results from the reactions of sulphonyl-substituted trienes. The stereochemistry of the major cis-fused cycloadduct is determined by single-crystal X-ray analysis of that obtained from reaction of racemic 4.     

Diversification of shotgun process

Three protocols for shotgun process are put forth in which simultaneous multi-fold reactions occur exclusively to each other. The first one involves simple combination of selective and non-selective reactions. Even if the simple protocol fails to give rise to the high selectivity, satisfactory outcome can be achieved by kinetic control or adjustment of functional groups.     

Correct structures of Diels-Alder adducts from the natural cyclolignan thuriferic acid and its 8-epimer

A detailed analysis of one- and two-dimensional ¹H and ¹³C NMR data for the endo and the exo adducts, obtained by Diels-Alder reaction of thuriferic and epithuriferic acids with cyclopentadiene is described. The unequivocal spectral data assignment of the endo and exo structures was complemented with molecular modelling studies and confirmed through X-ray diffraction studies.     

Cycloaddition reactions of β-trifluoroacetylvinyl ethers

β-Trifluoroacetyl vinyl ethers ROCHCHCOCF₃ react smoothly as dienophiles with α,β-unsaturated carbonyl compounds to give the unexpected 2-alkoxyl-5-trifluoroacetyl-3,4-dihydro-2H pyrans. These products are formed by elimination and addition of the alcohol to the products of the normal hetero Diels-Alder reaction (2-alkoxyl-3-trifluoroacetyl-2,3-dihydro-2H pyrans). In contrast, 1,3-dipolar cycloaddition of ROCHCHCOCF₃ with ArCHN(O)Me proceeds via a Z-endo transition state to give regio- and stereospecific 4-trifluoroacetyl substituted isoxazolidines and their derivatives.