Enantioselective Diels−Alder Cycloadditions with (SS)-2-(p-Tolylsulfinyl)-1,4-naphthoquinone:  Efficient Kinetic Resolution of Chiral Racemic Vinylcyclohexenes

Abstract

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Enantioselective Access to Key Intermediates for Salvinorin A and Analogues

“…In the case of 7a-c, the resulting cycloadducts 12a-c were isolated with high yields (85-90 %). As could be expected from previous work, [24] we observed a kinetic resolution at the benzylic position of the diene during the cycloaddition, which depended on the nature of the substituents. Excess of diene 7 was recovered as an S-(-)-enantioenriched mixture, showing that the R-(+)-enantiomer of 7 was more reactive; this is in complete agreement with known models (see Scheme 4).…”

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

“…90 When chiral racemic vinylcyclohexenes bearing allylic and nonallylic oxygenated substituents were used, the same reaction sequence took place to produce enantiomerically enriched tetracyclic quinones arising again from an efficient kinetic resolution of the dienes. 91 The same Diels-Alder/kinetic resolution strategy was applied in the synthesis of the angucyclicone antibiotics (+)-ochromycinone 124a and (+)-rubiginone B 2 124b where this highly efficient process accounts for the construction of the tetracyclic framework ( Figure 5). 92 Similarly, an access to a C3-oxygenated angucyclinone-type skeleton was devised and allowed the synthesis of enantiomerically enriched (-)-8-deoxytetrangomycin 125.…”

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. A double asymmetric induction process, where the matched pair in the cycloaddition corresponded to the (R) enantiomer of the sulfinyl-dienophile 5 or 6 reacting with the enantiopure diene (3S,5R,4S)-4 (TSI, Figure 4).…”

“…[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. As a result, using adequately substituted dienes, a one-pot enantioselective formation of the angucyclinone framework [16] occurred.…”