Scheme 1

Linear synthesis of LNA-U monomer [ 11 ]. Reagents (% yields): (i) Cyclohexanone, PTSA (quantitative); (ii) 2-iodobenzoic acid, CH₃CN (76%); (iii) (a) 37% HCHO, 2N NaOH, 1,4-dioxane; (b) NaBH₄ (38%); (iv) (a) TsCl, Pyridine; (b) TFA, water (34%); (v) PhCHO, ZnCl₂, (80%); (vi) NaBH₃CN, TiCl₄, CH₃CN (75%); (vii) NaHMDS, THF (61%); (viii) 10% Pd-C, H₂, MeOH (quantitative).