The ene reaction involving a carbonyl compound, an aldehyde in particular, as an enophile should, in principle, constitute a more efficient alternative to the carbonyl addition reaction of allylmetals which has now become one of the most useful methods for acyclic stereocontrol. We describe herein the new efficient methods for acyclic stereocontrol based on the carbonyl-ene reaction promoted or catalyzed by the Lewis acid. The carbonyl-ene reactions are shown to provide high levels of diastereocontrol, diastereofacial control, olefinic stereocontrol, and/or catalyst-based enantiofacial control, depending heavily on the characteristic feature of the achiral or chiral Lewis acid employed. Thus, the carbonyl-ene methodology is more advantageous than the allylmetal methodology for acyclic stereocontrol in terms of the easy availability of the olefin (ene) and the operational simplicity, along with the high levels of stereoselection.
This article reviews our own work on the recent development of the methodology for chiral preparation of nitrogen-containing natural products including alkaloids, antibiotics etc. utilizing 4-O-benzyl-2, 3-O-bis (methoxymethyl) -L-threitol (1), readily available from L-tartaric acid, as a common chiral synthon. The strategy for the natural product synthesis is based on regulating the stereochemical course of nucleophilic addition to the α, β-bis [(methoxymethyl) oxy] carbonyl and imino systems with highly selective diastereofacial differentiation in chelation or nonchelation processes, which are predictable. Also, this approach has allowed us to demonstrate the marked versatility of 1 as a synthetically very flexible chiral building block.
Studies on the synthesis and molecular structures of multibridged ferrocenophanes with tri-, tetra-and penta-methylene chains are described. [4n] Ferrocenophanes (n=2-5) were synthesized by stepwise construction of tetramethylene chain bridges via bridging reaction and insertion of a methylene unit. The molecule of the ultimate pentabridged compound,  superferrocenophane, resembles a Japanese pumpkin, according to the X-ray crystal structure. The conformation of the methylene chains of the superferrocenophane was analyzed by molecular mechanics calculation. Synthesis of  (1, 2, 3, 4) - and   (1, 2, 3, 4, 5) ferrocenophanes were achieved by the procedure based on a working hypothesis that was derived from a correlation between molecular structure and selectivity of bridging reaction of ferrocenophanealkanoic acids.   Ferrocenophane can become a synthetic precursor for  superferrocenophane. [5n] Ferrocenophanes (n = 2-4) were synthesized by repetition of bridging reaction and insertion of two methylene units. The electronic spectra of various multi-bridged ferrocenophanes revealed that the d-d absorption band underwent a proportionately hypsochromic shift with increase of the number of the tetramethylene bridge and with shortening of Cp ring-Fe-Cp ring distance.
On irradiation in a chlorinated hydrocarbon containing a catalytic amount of 9, 10-dicyanoanthracene (DCA), a polysilane causes chlorinative cleavage to give the corresponding chlorosilane (s) along with hexachloroethane. Intervention of the silyl radical cation is readily rationalized by the exothermic electron transfer from a polysilane to the excited singlet state of DCA, diffusion controlled quenching of the fluorescence of DCA with a polysilane, and formation of hexachloroethane. Cationic nature of the silyl radical cation is evidenced by intramolecular nucleophilic trapping by the hydroxyl group in polysilanylalkanols under these reaction conditions. A disilane undergoes regioselective photo-silylation of aromatic nitriles in two ways, namely, substitution of the nitrile, and that of the hydrogen. The position of the silyl group introduced is closely related to the substitution pattern of the nitrile, and the spin density of the radical anion. The tetraalkyl group 14 element compounds undergo similar regioselective photo-alkyl transfer to the aromatic nitrile. The natrue of the radical cation intervened is examined by means of a radical clock technique. The similarity of the pattern of the photoinduced electron transfer reaction to that of the mass spectrum of the organic group 14 element compound is also discussed.