A systematic investigation of the enantioselective Diels-Alder addition of 3-butenoyl-1,3-oxazolidin-2-one to cyclopentadiene under the influence of catalytic amounts of dichloro-Ti complexes of a,a,a',a'-tetraaryl-1,3-dioxolane-4,5-dimethanols (TADDOLs) is described. The influence of the mode of catalyst preparation, amount of catalyst, presence of molecular sieves, concentration of the reactands, temperature, solvent, and TADDOL structure on this reaction is studied. Best results (enantiomer ratio er 94:6) are obtained with the TADDOL-bearing Arl = C& and CsHj/CH3 substituents in the dioxolane 2-position (47) and with the Cz-symmetrical TADDOL with Arl = 2-naphthyl and two CH3 groups on the dioxolane 2-position (16). A surprising reversal of the absolute topicity of the reaction is observed with TADDOLs (15,28,32,38) bearing four 1-naphthyl groups: the 2(R)-instead of the 2(S)-bicyclo[2.2.1]hept-5-en-2-carboxylic acid derivatives are formed with enantioselectivities of up to 86:14. The crystal structures of several TADDOLs (16, 28, 47) and of the tetracyclohexylanalog 50 are described and compared with previously determined structures. A superposition of 29 structures reveals that the cyclic array of atoms of the TADDOLate moiety always has two axial and two equatorial aryl groups in a A-type conformation when derived from (R$)-tartrate and in a 8-type conformation when derived from (S,S)-tartrate. The binaphthols (BINOLs) show similar structural features (A in (P) or (SI and d in (MI or ( R ) enantiomers). A mnemonic rule is disclosed which applies to the steric course of Ti-BINOLate-and Ti-TADDOLatemediated reactions involving monodentate and bidentate electrophiles. The possible structure of the reactive complex involved in enantioselective reactions mediated by Ti-BINOLates and -TADDOLates, i.e., inter-and intramolecular [2 + 21 and [4 + 21 cycloadditions and ene reactions, is discussed.

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HRMS (M + HIt calcd for C28H36N306 510.2604, found 510.2608. Diasteromer 20b was prepared from 19b exactly as described above: HPLC tr = 8.62 min; 'H NMR (CD30D) 6 8.24 (s, lH), 7.27-7.12 (m, 5H), 7.07 (d, J = 8.1, 2H), 6.74 (d, J = 8.3, 2H), 4.59 (dd, J = 4.6, 9.6, lH), 4.16 (m, lH), 4.04 (m, lH), 3.96 (d, J = 5.9, lH), 3.22 (m, lH), 2.98-2.86 (m, 3H), 2.35 (m, lH), 1.96 (m, 2H), 1.74 (m, 2H), 1.55 (m, 3H), 1.44-1.17 (m,

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