Influence of the Sulfinyl Group on the Chemoselectivity and π-Facial Selectivity of Diels−Alder Reactions of (S)-2-(p-Tolylsulfinyl)-1,4-benzoquinone

Abstract

Diels-Alder reactions of (S)-2-(p-tolylsulfinyl)-1,4-benzoquinone (1a) with cyclic (cyclopentadiene and cyclohexadiene) and acyclic dienes (1-[(trimethylsilyl)oxy]-1,3-butadiene and trans-piperylene) under different thermal and Lewis acid conditions are reported. Chemoselectivity (reactions on C(2)-C(3) versus C(5)-C(6) double bonds) is mainly related to the cyclic (on C(5)-C(6)) or acyclic (on C(2)-C(3)) structure of the diene. The high pi-facial selectivity observed could be controlled by choosing adequate experimental conditions.

Recent developments in chiral non-racemic sulfinyl group chemistry in asymmetric synthesis

“…The Diels-Alder reactivity of (S)-2-(p-tolylsulfinyl)-1,4-benzoquinone 111 has been extensively studied. 84 Interestingly, this compound reacts with cyclopentadiene under thermal conditions to afford a mixture of two adducts 112 and 113, both arising from endo approach of the diene on the two diastereotopic faces of the unsubstituted double bond (Scheme 42). The stereoselectivity of the reaction can be controlled by careful choice of the solvent and reaction conditions.…”

Asymmetric Synthesis of Rubiginones A2 and C2 and Their 11‐Methoxy Regioisomers

“…[13] When the diene partner was a chiral C-3 oxygenated vinylcyclohexene (C in Figure 3), the stereochemical course of the cycloaddition with enantiopure (SS)-2-(p-tolylsulfinyl)-1,4-naphthoquinone was a consequence of the preference for the anti approach of the diene, to the less hindered upper face of the scis conformation of the quinone. [15] On the basis of the above-mentioned model of approach and the experimental data, we propose that diastereomers 24 and 26, resulting from reaction between enantiopure diene 4 and racemic 5 or 6, must arise from transition state endo-anti-TSI, shown in Figure 4.…”

“…The strategy used was based on the ability of the sulfoxide to control the p-facial diastereoselectivity of endo cycloadditions of sulfinylquinones. [13] Moreover, the sulfinyl group triggered an efficient domino [14] process where the Diels-Alder reaction was followed by the elimination of the sulfoxide, that allowed to recover the quinone moiety in the resulting adduct. When the Diels-Alder reaction was run with a chiral racemic diene, [15] the enantiopure (SS)-2-(p-tolylsulfinyl)-1,4-naphthoquinone promoted a double asymmetric induction process leading to the efficient kinetic resolution of the diene.…”

Towards Configurationally Stable [4]Helicenes: Enantioselective Synthesis of 12‐Substituted 7,8‐Dihydro[4]helicene Quinones

“…[49,50] The additional helical chirality shown by compounds 16 ac and 17 c,d, evident from the X-ray structures of 16 a and 17 d, must be a consequence of the complete shift of the conformational equilibrium towards boat-like structure I in 16 a,b and II in 17 d, with the relative stability of conformers I and II dependent on the substituent at C-12 (R 1 in Scheme 13). In the case of the isopropyl-substituted derivative 16 c, we initially detected a structure in which the 1 H NMR spectroscopic parameters matched with conformer I.…”

“…[28c, 49] Thus, the initial Diels-Alder adduct must result from the preferred endo approach of the vinyl dihydronaphathalenes 6 a-d to the less-encumbered upper face of the sulfinylquinone (SS)-8, adopting the (s)-cis conformation represented in Scheme 14, usually the most stable and reactive of vinyl sulfoxides. [49,50] The additional helical chirality shown by compounds 16 ac and 17 c,d, evident from the X-ray structures of 16 a and 17 d, must be a consequence of the complete shift of the conformational equilibrium towards boat-like structure I in 16 a,b and II in 17 d, with the relative stability of conformers I and II dependent on the substituent at C-12 (R 1 in Scheme 13).…”