Diels-Alder reaction selectivity

The Diels-Alder Reaction Selected Practical Methods Edited by Francesco Fringuelli and Aldo Taticchi Copyright 2002 John Wiley Sons, Ltd ISBNs 0-471-80343-X (Hardback) 0-470-84581-3 (Electronic)... 

L. W. Butz and A. W. Rytina, Org. React., 5, 136 (1949) M. C. Kloetzel, Org. React., 4, 1 (1948) A. Wasserman, Diels-Alder Reactions, Elsevier, New York (1965) F. Fringuelli and A. Tatacchi, Diels-Alder Reactions Selected Practical Methods, Wiley, New York, 2001. 

Perhaps the most useful part of the reported synthesis is the facile preparation of (—)-pyrimidoblamic acid (12 Scheme 3). A key to this synthesis is the preparation of the fully substituted pyrimidine 8. This was done by a one-pot inverse electron demand Diels-Alder reaction between the symmetrical triazine 7 and prop-1-ene-1,1-diamine hydrochloride, followed by loss of ammonia, tautomerization, and loss of ethyl cyanoformate through a retro-Diels-Alder reaction. Selective low-temperature reduction of the more electrophilic C2 ester using sodium borohydride afforded 9, the aldehyde derivative of which was condensed with 7V -Boc-protected (3-aminoalaninamide to give the imine 10. Addition of the optically active A-acyloxazolidinone as its stannous Z-enolate provided almost exclusively the desired anti-addition product 11, which was converted into (—)-pyrimidoblamic acid (12). Importantly, this synthesis confirmed Umezawa s assignment of absolute configuration at the benzylic center. 

Diels-Alder reaction selectivity Me3Si < (/-Bu)Me2Si < (y-Pi)3Si 85... 

F. Fringuelli and A. Taticchi, The Diels Alder Reaction. Selected Practical Methods, John Wiley Sons, Ftd, New York, 2002. 

The Diels Alder reaction selected practical methods / Francesco Fringuelli, Aldo Taticchi. p. cm. 

Moreover, after screening several additives other than 29, it was found that some additives were effective not only in stabilizing the catalyst but also in controlling the enantiofacial selectivities in the Diels-Alder reaction. Selected examples are shown in Table 25. When 3-acetyl-l,3-oxazolidin-2-one (30) was combined with the original catalyst system (to form catalyst A), the endo adduct was... 

Moreover, after screening several additives other than 31, it was found that some additives were effective not only in stabilizing the catalyst but also in controlling the enantiofacial selectivities in the Diels-Alder reaction. Selected examples are shown in table 29. When 3-acetyl-l,3-oxazolidin-2-one (32) was combined with the original catalyst system (to form catalyst A), the endo adduct was obtained in 93% ee and the absolute configuration of the product was 2S, 3R. On the other hand, when acetyl acetone derivatives were mixed with the catalyst, reverse enantiofacial selectivities were observed. The endo adduct with an absolute configuration of 2R, 3S was obtained in 81% ee when 3-phenylacetylacetone (PAA) was used as an additive (catalyst B). In these cases, the chiral source was the same (Tf)-binaphthol. Therefore, the enantioselectivities were controlled by the achiral ligands, 3-acetyl-l,3-oxazolidin-2-one and PAA (Kobayashi and Ishitani 1994). 

Fringuelli, F. Tatchi, A. In The Diels Alder Reaction Selected Practical Methods John Wiley Sons Ltd. West Sussex, England, 2002. 

---