Development of Chiral Ferrocenyl Compounds including Hetero Atoms and Their Use in Asymenetric Synthesis

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We have developed the methodology to introduce chilalities into organic molecules using chiral ferrocenylselenium reagents. These reagents are applicable to asymmetric synthesis of chiral compounds such as allenes, 4-alkyl-1-alkylidenecyclohexanes, b-hydroxyalkyl selenides, allylic alcohols, and allylic amines. In this report we present new methodology to prepare several heterocycles with a high stereoselectivity. Asymmetric intramolecular selenocyclization of alkenoic acids, alkenols, and alkenyl urethanes using optically active 2-[1-(dimethylamino)ethyl]ferrocenylselenenyl cations proceeds smoothly to give the corresponding organoselenenyl moiety containing lactones, cyclic ethers, and N-heterocycles, respectively, in good to excellent chemical yields (up to 97%) with very high diastereoselectivities (up to 98% de). The nature of counter anions of the selenenylating agents affected remarkably the diastereoselectivity of the cyclization, PF_6 and BE_4 being revealed to be the best for that of alkenoic acids and alkenols and that of alkenyl urethanes, respectively. The plausible reaction scheme for cyclization is presented where a chiral selenenylating agent approaches the carbon-carbon double bond of the substrate from the less bulky direction to afford a chiral episelenonium ion followed by an intramolecular back side attack of a nucleophile.