1.7.9- Decatriene Diels-Alder reactions

The intramolecular Diels-Alder reaction of 2-methyl-( , )-2,7,9-decatrienal catalyzed by the CBA catalyst 3 proceeds with the same high diastereo- and enantio-selectivity [5d] (Scheme 1.6). 

Brmsted acid-assisted chiral Lewis acid 8 was also applied to the intramolecular Diels-Alder reaction of an a-unsubstituted triene derivative. ( , )-2,7,9-Decatrienal reacts in the presence of 30 mol% of the catalyst to afford the bicyclo compound in high yield and good enantioselectivity [lOd] (Scheme 1.17). 

LP-DE also promotes and accelerates intramolecular Diels-Alder reactions of low reactive polyenones. The use of a catalytic amount of camphorsulfonic acid (CSA) further accelerates the cycloaddition and enhances the diastereo-selectivity [41]. Table 6.7 illustrates the effect of CSA on the intramolecular Diels-Alder reaction of 2-methyl-l,7,9-decatrien-3-one. 

Table 6.7 Intramolecular Diels-Alder reaction of 2-methyl-l,7,9-decatrien-3-one...

P. Herczegh, M. Zsdby, L. Szil gyi, Z. Dinya, and R. Bogndr, High diastereoselectian in the intramolecular Diels-Alder reaction of sugar-based 1,7(BZ),9-decatrienes, Tetrahedron 45 5995 (1989). 

The increased stereoselectivity of decatrien-3-ones relative to the n(matrien-3-ones may also be the consequence of cooperativity between twist asynchronicity and endo stabilization that both favor the c -fused product. The decatrien-3-one transitirm state is considerably less strained than the nonatrien-3-one transition state, and the uncatalyzed decatrienone cyclizations occur at or near ambient temperature. Consequently, one expects greater endo stabilization, and hence also greater cis stereoselectivity, in the decatrienone intramolecular Diels-Alder reactions. 

An enantioselective intramolecular Diels-Alder reaction of a-unsubstituted 2,7,9-decatrienal afforded the corresponding bicychc aldehyde in high yield and... 

Tab. 2.8. Volume data of the intramolecular Diels-Alder reactions of nonatriene (E)-42 and decatriene (f )-45.

To assess the diastereoselectivity and the intrinsic reactivity of prosolanapyrones, Diels-Alder reactions were examined under various conditions." In less polar solvents, heating was required for the effective cycloaddition of 136—138. Increase in the oxidation levels of the three substituents in the prosolanapyrones enhances rate acceleration. This can be rationalized in terms of the LUMO energy of the dienophile moiety in the pyrone precursors. Wo-/cxo-selectivities with 136—138 were essentially the same in various organic solvents, while the wt /o-selectivity was increased with increasing solvent polarity. The slight preference for f zfo-selectivity in less polar solvents suggests that there is little steric congestion in both endo- and cxo-transition states as reported in the reactions of simple decatriene systems." ... 

Chiral thiopyran derivatives have been obtained in Diels-Alder reactions from monosaccharide O-thioformates and dithiooxalates. Intramolecular Diels-Alder cyclization of 1,6,8-nonatrienes and 1,7,9-decatrienes prepared from pentoses or D-glucose afforded multichiral hexahydroindene and octahydronaphthalene derivatives with very high diastereoselectivity. 

Intramolecular Diels-Alder (IMDA) reactions of 1,6,8-nonatrienes and 1,7,9-decatrienes have been used frequently for the construction of chiral ring systems of complex natural products (18-20), Although saccharide derivatives have been employed many times in intermolecular Diels-Alder reactions (21-28) their IMDA reaction appears not to have been studied so far. The diastereoselectivity of IMDA reactions can be influenced, among other factors, by the size of substituents, and by the chirality of carbons of the connecting chain. Our aim was to study the possibilities of the application of single monosaccharides as tether chains in IMDA reactions. The influence of the presence of three or four chiral... 

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