Several excellent methods have been devised for acyclic stereocontrol over 1, 2- and 1, 3-asymmetric relationships. However, approaches to control remote 1, >3-relationships are rare. Hence the development of methods for remote stereocontrol has remained as one of the most challenging problems in organic synthesis. The methods for remote stereocontrol are conceptually divided into six different types; (a) “coupling” of chiral synthons; (b) “removal” of chiral centers from a chiral pool to keep the remote chiral centers; (c) “chirality transfer” of the adjacent chiral center (temporarily introduced) to the remote position by sigmatropic rearrangements or stereospecific substitution reactions with organometallic reagents; (d) “asymmetric synthesis” without any communication of the pre-existing chiral center; (e) “relative asymmetric induction” with stereo-communication of the pre-existing chiral center; (f) “internal asymmetric induction” over the new and remote chiral centers during C-C bond formation. The last two methodologies are relatively new comers and hence this review is focused on these two methodologies which are based on chelation control, vinylogous stereoelectronic (Cram's) control, neighboring group participation, orbital control, and so forth.
Diastereoselective addition of nucleophiles to carbonyl and imine compounds with α- and/or β-substituents has been a valuable tool in the synthesis of complex molecules. Since optically active epoxides are easily accessible by Sharpless asymmetric epoxidation, the utiltiy of this group as a stereocontrolling element in such reactions is getting more and more highlighted recently. This account surveys diastereoselectivities in the nucleophilic additions to the C = X bonds found in i) α, β-epoxy aldehydes, ii) α, β-epoxy ketones, iii) α, β-epoxy imines, and iv) γ, δ-epoxy-α, β-unsaturated carbonyl compounds (conjugate addition) in this order and also presents some devices to achieve high selectivities as well as possible rationale of the stereochemical outcome in certain cases. Application of these reactions to the synthesis of biologically active compounds is also illustrated.
This article deals with a compilation of recent developments in the asymmetric synthesis of versatile chiral building blocks and with their application to the natural product syntheses carried out in our laboratories. The asymmetric construction of a versatile chiral building block for biologically active natural and non-natural compounds would provide us with powerful tools for the syntheses of these molecules. As one of the efforts to make a breakthrough for the enantioselective alkaloid synthesis, we designed, as chiral educts, some piperidines, pyrrolidines, and pyrrolidones provided with versatile functionality. These chiral azacycles were constructed by using an asymmetric intramolecular Michael reaction, the Katsuki-Sharpless asymmetric epoxidation followed by sequential regioselective amination and intramolecular cyclization, and the asymmetric cleavage of σ-symmetric 'fork head ketone'systems, respectively. The resulting chiral building blocks were converted to Rauwolfia alkaloids (e.g. ajmalicine, tetrahydroalstonine, and yohimbine), an unusual amino acid (e.g. bulgecinine), and indolizidine alkaloids (e.g. monomorine I and indolizidine 223 AB), respectively.
Polysaccharides such as cellulose and amylose are the most accessible optically active polymers. The polysaccharides themselves show rather low chiral recognition, but their derivatives show high chiral recognition and afford useful chiral stationary phases (CSPs) for HPLC. In this review, optical resolution by cellulose esters, especially benzoates, and by various phenylcarbamates of cellulose and amylose is discussed. Chiral recognition abilities of aralkylcarbamates of cellulose and amylose are also evaluated.
Ring expansion reaction is one of the excellent methods for construction of medium- and large sized cyclic compounds. In present review, the so-called “zip” ring expansion has been focussed to synthesize carbocyclic or heterocyclic compounds. The reaction proceeds under a basic media (or radical process) via one-pot two-steps sequence from α, α-disubstituted cyclic ketones with a nucleophilic side chain;i) addition of intramolecular nucleophile (or radical) to carbonyl function to construct a bicyclo[m.n.0] skeletal intermediate;ii) cleavage of bridged bond to afford [m+n]-membered products.
Photocyclization provided a good route to prepare azonia derivatives of fused polycyclic aromatic compounds such as benzo [c] phenanthrene, benzo [ghi] perylene, benzo [a] coronene, picene, and  helicene. The photoreactions could be classified into four types; (A) photocyclization of 1-styrylpyridinium salts to benzo [a] quinolizinium derivatives, (B) photocyclizaiton of styrylquinolizinium salts to fused azonia compounds, (C) photocyclization of 2-styrylpyridine derivatives to benzo [c] quinolizinium salts, and (D) photocyclization of 1, 2-diarylpyridinium salts. The photocyclization occurred when the bond order (Prs*) between atoms r and s, involved in the cyclization in the excited state, has a negative value.