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Steroids Steroids U 0300Preparation of a Novel 16-DPA-P 2 S 5 Adduct and Its Application as a Masked α,β-Unsaturated Ketone in [4 + 2] Cycloaddition Reactions. -Attempted thionation of 16-dehydropregnenolone acetate (I) with P 4 S 10 results in formation of the dimer (II) instead of the expected thione. The dimer undergoes [4 + 2] cycloaddition with alkynes to yields the pyrans (IV). -(CHETIA, A.; SAIKIA, A.; SAIKIA, C. J.; BORUAH*, R. C.; Tetrahedron Lett. 44 (2003) 13, 2741-2744; Div. Med. Chem., Reg. Res. Lab., Jorhat 785 006, India; Eng.) -Mais 26-198