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[摘要]：Alkynyl- and alkenylselenonium salts reacted with nucleophiles at the alpha- or beta-carbon depending upon the nucleophiles. The alpha-attack caused the addition-elimination reaction; i.e., the apparent substitution reaction and the beta-attack (the conjugate addition) generated an ylide, which brought about the tandem reaction to form a variety of heterocyclic compounds. Some new reactions proceeded via the selenuranes formed by the attack of a nucleophile on the positively charged selenium atom. An interesting tandem Michael-aldol reaction of enones (ynones) bearing a chalcogenide or a thioamide was developed. The reactions of the 1-[2-(methylchalcogeno)phenyl]propenones gave alpha-(alpha-hydroxyalkyl)enones (Morita-Baylis-Hillman adducts) after a work-up with Et3N. The reactions of the 3-cinnamoy1-1,3-oxazolidine-2-thiones with aldehydes gave tricyclic compounds with a bridgehead bound to four heteroatoms. The asymmetric reactions simultaneously induced four stereocenters, three of which are contiguous. Removal of the chiral auxiliary provided 1,3-diols bearing three consecutive stereocenters. |
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