| Research Abstract |
The author originally prepared some 4-alkoxy-1,3-butadienes bearing 1,2-bis(sulfanyl)-or 1-selanyl-2-sulfanyl groups as starting materials of 4-carbon homologations. Treatment of the phenyl propargyl sulfides or selenides with ethyl magnesium bromide/triethyl ortho formate provided 4-sulfanyl or 4-selanylbut-2-ynal diethyl acetals in good yields. The isomerization with sodium alkoxide and the successive addition of sodium benzenethiolate or selenolate to give the 3,4-bis(sulfanyl)-or 4-selanyl-3-sulfanylbut-3-enal diethyl acetals. The dealkoxylation of the acetals exclusively formed the 4-alkoxybuta-1,3-dienes. Next, we tried our usual methodology consisting of the Wittig type two-step procedure, using 4-alkoxybuta-1,3-dienes. The lithiation of the 1-phenylsulfanyl-4-alkoxybuta-1,3-dienes proceeded at 1-position with DABCO/n-BuLi or LTMP and reactions with aldehydes provided the pentadienol derivatives in moderate yields. The acid-promoted hydration underwent cycization to give the 5-membered ring compounds ; however, the penta-2,4-dienals were obtained in low yields. We precisely investigated the hydration step and SOCl_2/pyridine found to be effective for formation of the penta-2,4-dienals. Some aldehydes provided the penta-2,4-dienal derivatives in good yields ; however, the stereoselectivities of the products are not good. We also performed the tandem penta-2,4-dienylation of the aldehydes using 4-alkoxybuta-1,3-dienes. The second penta-2,4-dienylation provided 2,4,6,8-tetrakis(phenylsulfanyl)nona-2,4,6,8-tetraenal derivative, which was isolated as its hydrazone derivatives. Now, we are investigating the characterization of the nona-2,4,6,8-tetraenals, especially the photo-chemical behaviors.
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