Cyclic Vinyl p-Tolyl Sulfilimines as Chiral Dienophiles:  Diels−Alder Reactions with Furan and Acyclic Dienes

Abstract

The dienophilic behavior of the sulfilimine 2, synthesized from (Z)-3-p-tolylsulfinylacrylonitrile 1, in its Diels-Alder reactions with furan and acyclic dienes has been investigated. A complete pi-facial selectivity for 2, opposite to that observed from its precursor 1, is the main feature of all these cycloadditions. Moreover, the high exo selectivity observed in reactions of 2 with furan (not observed for 1) contrasts with the almost complete endo selectivity with other cyclic and acyclic dienes. Additionally, the opposite regioselectivities obtained for 2 with Dane's diene and 1-substituted butadienes (not observed for 1) are also noteworthy. This behavior allows dienophiles 1 and 2 to be considered as complementary precursors from a synthetic point of view.

Search for ideal sulfinyl dienophile and dipolarophile

“…Thus, 1-methoxybutadiene evolved into just one endo adduct, which could be isolated in 89% yield, at 4 Kbar under ZnBr 2 catalysis [21]. As can be seen in Fig.…”

“…• C under BF 3 catalysis to afford the exo adduct in 85% isolated yield of diastereomerically pure product, the de of the process being 92% [21]. The reasons determining the strong exo selectivity of the sulfilimines are not so clear, specially after demonstration that the equilibration between the endo and exo adducts does not take place under the reaction conditions, which excludes the obtention of the exo adducts as a result of a thermodinamically controlled Diels-Alder reaction.…”

“…13, the endo and π-facial selectivities, as well as the regioselectivity were complete. Piperylene evolved in a similar stereochemical way, although the regioselectivity was not complete, yielding an 8:1 mixture of regioisomers [21].…”

3‐Amino‐Substituted Isothiazole S,S‐Dioxides as Dienophiles in Diels–Alder Cycloaddition Reactions with Cyclic, Acyclic and Heterocyclic Dienes

“…[8] As a confirmation, a sample of a mixture of exo-and endo-15 (1:5) was independently treated with furan in a sealed tube at 80°C (Entry 8), and the reaction mixture was analysed by 1 H NMR spectroscopy every 30 min. The spectra show a progressive change of the exo/endo ratio in favour of the exo isomer, which indicates that a retro Diels-Alder reaction takes place.…”

“…In principle, the lack of an aromatic ring at C-4 in compound 6 could influence the reactivity of the system substantially, both by altering the electronic distribution at the C-4=C-5 double bond and strongly reducing the steric hindrance. 2,3-Dimethylbutadiene (7), cy-clopentadiene (8) and furan (9) were chosen as representatives of the main classes of dienes, i.e. acyclic, cyclic and heterocyclic ones, respectively.…”