Synthesis of pyrrol-2-yl- and pyrazol-4-ylmethylidene derivatives of betulin and allobetulin

Aldol-crotonic condensation of allobetulone and betulonic aldehyde with N -substituted pyrrole-2- and pyrazole-4-carbaldehydes afforded a series of new α,β-unsaturated ketones of lupane series. Their reduction provided 2-ylidene derivatives of allobetulin and betulin, potential chiral components of liquid crystal materials. Structures of 1-phenyl-3-(4-phenoxyphenyl)-1 H -pyrazole-4-carbaldehyde, ( E )-2-{[3-(4-methoxyphenyl)-1-phenyl-1 H -pyrazol-4-yl]methylidene}allobetulone, ( E )-2-{[3-(4-bromophenyl)-1-phenyl-1 H -pyrazol-4-yl]methylidene}-3-oxolup-20(29)-ene-28-carbaldehyde, ( E )-2-{[3-(4-bromo-phenyl)-1-phenyl-1 H -pyrazol-4-yl]methylidene}allobetulin, and ( E )-2-{[3-(4-bromophe-nyl)-1-phenyl-1 H -pyrazol-4-yl]-methylidene}lup-20(29)-ene-3,28-diol were established by X-ray diffraction (XRD) study.