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Intramolecular Hetero‐Diels–Alder Reactions of Oxadienes: Influence of Substituents of the Tether on the Diastereoselectivity

1990; Wiley; Volume: 29; Issue: 6 Linguagem: Inglês

10.1002/anie.199006651

1521-3773

Lutz F. Tietze, Siegbert Brand, Thomas Brumby, Jens Fennen,

Molecular spectroscopy and chirality

How do substituents on the chain of 1 influence the stereosclectivity of the intramolecular hetero-Diels-Alder reaction? This question was followed up by exact analysis of the product composition of the reactions of 1 a and its methyl analogues 1 b–e with 2 to give 3a–e. It emerged that "steric" and "conformational" effects in the chair-shaped transition structure must be differentiated and that the equatorial position of the methyl group is more strongly favored in the transition structures leading to 3c, d than in methylcyclohexane. R = H (a), α-Me (b), β-Me (c), γ-Me (d), δ-Me (e).