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The synthesis of the first polymer-supported TADDOL is reported. Its efficiency as chiral ligand of Ti(IV) was studied in the Diels-Alder cycloaddition of cyclopentadiene to 3-crotonoyl-1,3-oxazolidin-2-one, and was superior to that observed for its homogeneous equivalent, (4R,5R)-␣,␣,␣Ј,␣Ј-2-pentaphenyl-4,5-dimethanol-1,3-dioxolane. Recycling of the heterogeneous Ti(IV)-TADDOLate was also studied, being the most suitable method for the repreparation of the catalyst from the ligand after use. Chirality 9:191-197, 1997. © 1997 KEY WORDS: TADDOL; titanium complexes; chiral Lewis acid; polymer-supported; polystyrene-divinylbenzene; enantioselective; Diels-AlderThe Diels-Alder reaction is probably the most important synthetic method for obtaining cyclohexenes and is the key step in the synthesis of a large number of natural products.1 in the last few years, the asymmetric Diels-Alder reaction using chiral catalysts has been widely studied. [2][3][4] Especially interesting are the chiral Ti(IV) reagents derived from an achiral Ti(IV) Lewis acid and a 1,4-diol of general structure ␣,␣,␣Ј,␣Ј-tetraaryl-1,3-dioxolane-4,5-dimethanol 4,5 (TADDOL, Fig. 1). This family of compounds has proved to be an effective chiral catalyst not only in Diels-Alder reactions 6-8 but also in other types of reactions such as nucleophile addition to aldehydes, 4,9 enereaction, 10,11 [2+2] cycloadditions, 12 1,3-dipolar cycloaddition, 13 and hydrocyanation of aldehydes. 14 Very recently Greeves and co-workers 15 have reported the use of TADDOLs as chiral ligands for enantioselective addition of organocerium regents to aldehydes.Since the pioneering work of Merrifield 16 in solid-phase synthesis, much effort has been made in the development of new applications. Recently, attention has been focused in polymer-supported chiral catalysts because of the advantages implied: ease of chiral auxiliary isolation, ease of recovery and applicability in flow systems.Several polymeric chiral Lewis acids have been developed for asymmetric alkylations, [17][18][19] reductions, 20 or epoxidations, 21 but to our knowledge only Itsuno and coworkers 22 have synthesized effective polymeric chiral catalysts for enantioselective Diels-Alder reactions. These authors have studied the efficiency of several Nsulfonylamino acids, amino-alcohols, and diols anchored to an insoluble support as ligands of boron in the cycloaddition of cyclopentadiene to methacrolein, being 65% enantiomeric excesses (e.e.) 22a the best optical yield reached for the exo cycloadduct.Following our previous work on the enantioselective Diels-Alder reaction, 8 we report the synthesis of the polymer-supported TADDOL 1 (P-TADDOL, heterogeneous equivalent of (4R,5R)-␣,␣,␣Ј,␣Ј-2-pentaphenyl-4,5-dimethanol-1,3-dioxolane (2) (Fig. 2)), and its efficiency as a chiral ligand of Ti(IV) in the Diels-Alder addition of cyclopentadiene to 3-crotonoyl-1,3-oxazolidin-2-one. MATERIALS AND METHODS1 H-NMR spectra were recorded on a Varian-Gemini 300 spectrometer (Palo Alto, CA) at 300 MHz, in CDCl 3 , and ...

. 5-Ethyl-5,6-dihydro-llH-dibenzo[b,e]azepine-6-thione has been synthesized and studied in the solid state and in solution by X-ray diffraction and 'H DNMR, respectively. The crystals are monoclinic, P21/rz, a = 9.642(1), b = 13.757(2), c = 9.889((2) A, p = 98.57(1)", Z = 4. The structure has been solved by direct methods and refined to an R value of 0.040 for 177 1 reflections with I > 2.5u(l). The seven-membered ring has a slightly deformed boat conformation. The activation barrier associated with the inversion ring has been determined, being A& = 2 1.6 kcallmol. (2) A, p = 98,57(1)", Z = 4. La structure a Ct C rCsolue au moyen de mCthodes directes et raffinCe h une valeur de R = 0,040 par 1771 reflexions avec 1 > 2,5u(l). Le cycle heptagonal a une conformation bateau 1Cgkrement dCformCe. La barrikre d'activation associCe avec I'inversion du cycle a Ct C determinte, Ctant A& = 21,6 kcallmol.

The perchlorotriphenylmethyl radical (PTM) shows enantiomerism due to restricted internal rotations. Several chiral stationary phases have been tested in different conditions for the resolution of PTM by HPLC. Only poly(triphenylmethy1 methacrylate) provided sufficient resolution for canying out a micropreparative scale separation. Racemization of (+)-and (-)-PTM was monitored polarimetrically as a function of time. The process was found to follow strict first-order kinetics. The value of AGX303.8 = 23.6 Kcal * mol-' agrees with that determined previously by HPLC with the stopped flux technique (Crespo, Doctoral Thesis, CETS Institut Quimic de Sarrii, 1991). Following the helicity rules in the circular dichroism spectrum, (+)-PTM can be assumed to have (P) configuration and (-)-PTM (M) configuration. o 1995 Wiey-Liss, h c .