Solid-phase synthesis reduction reactions

The classic Reissert indole synthesis, involving the reductive cyclization of o-ni-trophenylpyruvic acid, has been used for synthesis of 2-ethoxycarbonyl-4-alkoxymethylindo-les.92 The modified Reissert reaction, involving the reductive cyclization of an o-nitrophenyl acetoaldehyde, has been adapted to solid-phase synthesis.93... 

In solid-phase synthesis the standard conditions used in solution resulted in an incomplete reaction probably due to a swelling problem of the resin in MeOH. In this case the use of DMF in place of MeOH results in an approximately complete reaction. 7 It has been shown that the introduction of a reduced amide linkage between Phe and Pro residues, by reductive alkylation of the Pro nitrogen with Boc-Phe-H in the presence of NaBH3CN under acidic conditions leads to epimerization of the Phe residue. 57 This problem of racemization is... 

Ley SV, Mynett DM, Koot WJ, Solid phase synthesis of bicyclo[2,2,2]octane derivatives via tandem Michael addition reactions and subsequent reductive amination, Synlett., 1017-1020, 1995. 

Kamal and co-workers have reported a new approach for the solid-phase synthesis of the pyrrolo[2,l-c][l,4]benzodiazepines 102 using a thiol Wang resin. The interesting feature of this approach was the reductive cleavage and cyclization achieved in the last step on reaction with DIBAL-H yields of the products 102 ranged from 57% (R = 7-OMe, 8-OBn) to 65% (R = H) <04TL7667>. 

---