1,4-REMOTE AND 1,5-REMOTE STEREOCONTROL VIA RELATIVE AND INTERNAL ASYMMETRIC INDUCTION

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.