Bull-free Berge graphs are perfect

Abull is the (self-complementary) graph with verticesa, b, c, d, e and edgesab, ac, bc, bd, ce; a graphG is calledBerge if neitherG not its complement contains a chordless cycle whose length is odd and at least five. We prove that bull-free Berge graphs are perfect; a part of our argument relies on a new property of minimal imperfect graphs.This work was done while both authors were at the School of Computer Science, McGill University; support by NSERC is gratefully acknowledged.     

Heterogeneous diastereoselective hydrogenation of pyridine and corresponding enamine covalently bound to pantolactone

The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to pantolactone was studied over supported metallic catalysts. With this chiral auxiliary, a two-steps reaction was observed with formation of tetrahydropyridine intermediate. The influence of different reaction parameters on the diastereoselectivity of the hydrogenation of pyridine and enamine substrates was studied.     

Diastereoselective heterogeneous catalytic hydrogenation of 2-methyl nicotinic acid using pyroglutamate chiral auxiliary

The diastereoselective hydrogenation of 2-methyl nicotinic acid covalently bound to proline ester or pyroglutamic ester over supported metallic catalyst yielded moderate diastereoselectivity (26%). The hydrogenation of the corresponding pyridinium salt was studied and similar de's were achieved.     

Recognizing bull-free perfect graphs

A bull is the graph obtained from a triangle by adding two pendant vertices adjacent to distinct vertices of the triangle. Chvátal and Sbihi showed that the strong perfect graph conjecture holds for Bull-free graphs. We give a polynomial time recognition algorithm for Bull-free perfect graphs.