Complete π‐Facial Stereoselectivity in the TiCl₄‐Mediated [4 + 2] Cycloaddition of Cyclopentadiene to N,N′‐fumaroyldi[(2R)‐bornane‐10,2‐sultam]

Abstract

Under the co-operative influence of two prosthetic groups, and independent of the TiC1, concentration, complete and constant diastereofacial n -selection was achieved during the [4 + 21 cycloaddition of cyclopentadiene to N,N'-fumaroyl-di[(2R)-bornane-10,2-sultam] ((-)-lc); reactive conformations are discussed.

Influence of the Solvent Polarity on the Stereoselectivity of the Uncatalyzed [4+2] Cycloaddition of Cyclopentadiene toN,N′-Fumaroyldi[(2R)-borane-10,2-sultam]

“…After 4 ± 18 h, the solvent and the excess of cyclopentadiene were evaporated under medium, then high vacuum. The crude cycloadduct 2 (99% yield) was submitted to 1 H-NMR analysis for conversion and de determination [1]. TLC (hexane/AcOEt 7 : 3): R f ((À)-1).…”

“…First of all, if we consider that an energy difference of 2.5 kcal/mol in the transition state corresponds to the limit of detection of the 1 H-NMR analysis that we performed, we see that the minor diastereoisomer (2S,3S)-2, which results from C(a)-si attack, originates from the bis(syn-s-cis) conformation and possesses the smallest transition state intrinsic dipole moment. Leaving aside steric and stereoelectronic considerations related to the approach of the diene [3], this is thus the less disfavored transition state in apolar solvents 11 ).…”

“…of cyclopentadiene to 0.02m (À)-1 in the chosen solvent at 208. The p-facial selectivity was measured after 18 h, as earlier reported [1], directly by 1 H-NMR analysis at 500 MHz of the olefinic signals of the diastereoisomeric cycloadducts 2 in the reaction mixture.…”

Stereoselectivity in the TiCl4-Catalyzed [4+2] Cycloaddition of Cyclopentadiene to (2R)-Bornane-10,2-sultam Derivatives of Fumaric Acid Monoesters

“…± We recently presented the complete p-facial selectivity observed in the TiCl 4 -catalyzed [4 2] cycloaddition of cyclopentadiene to N,N'-fumaroylbis[(2R )-bornane-10,2-sultam] ((À)-1a) [1] under the influence of diverse Lewis acids, as well as its application to diverse dienes [2]. Although these kinds of cycloadducts have been employed for the synthesis of several natural products [3] and analogues [4], their use is usually limited to symmetric or specific targets where the two carbonyl moieties can be distinguished by either iodolactonization [5] or selective steric approach of the reagent 3 ).…”

“…For a detailed study of the [4 2] cycloaddition, dienophile (À)-1b was selected, anticipating a simpler 1 H-NMR analysis of the cycloadducts, as well as a potential S n 2' chemospecific saponification of the methoxycarbonyl moiety [19]. The uncatalyzed [4 2] cycloaddition of (À)-1b to cyclopentadiene (10 mol-equiv.)…”