We present our first results on the synthesis of a new class of conformationally restricted vitamin D analogues bearing an extra five-membered ring formed by linking C(18) and C(2 1). Two analogues of calcitriol (1) with unsaturations at the extra ring and the lateral chain were prepared. The triene system was introduced by the convergent Wittig-Horner approach developed by Lythgoe [8] and F. Hoffmann-La Roche [9]. The key steps in the preparation of the requisite fragments were: i) the long-distance functionalization of ketal 11 at C(18) ii) the ring closure on 15 through an intramolecular aldol condensation to give the alpha,beta-unsaturated ketone 10, and iii) the Pd-catalyzed installation of the side chains.
We present our first results on the synthesis of a new class of conformationally restricted vitamin D analogues bearing an extra five-membered ring formed by linking C(18) and C(2 1). Two analogues of calcitriol (1) with unsaturations at the extra ring and the lateral chain were prepared. The triene system was introduced by the convergent Wittig-Horner approach developed by Lythgoe [8] and F. Hoffmann-La Roche [9]. The key steps in the preparation of the requisite fragments were: i) the long-distance functionalization of ketal 11 at C(18) ii) the ring closure on 15 through an intramolecular aldol condensation to give the alpha,beta-unsaturated ketone 10, and iii) the Pd-catalyzed installation of the side chains.
We present our first results on the synthesis of a new class of conformationally restricted vitamin D analogues bearing an extra five-membered ring formed by linking C(18) and C(2 1). Two analogues of calcitriol (1) with unsaturations at the extra ring and the lateral chain were prepared. The triene system was introduced by the convergent Wittig-Horner approach developed by Lythgoe [8] and F. Hoffmann-La Roche [9]. The key steps in the preparation of the requisite fragments were: i) the long-distance functionalization of ketal 11 at C(18) ii) the ring closure on 15 through an intramolecular aldol condensation to give the alpha,beta-unsaturated ketone 10, and iii) the Pd-catalyzed installation of the side chains.