Sulfinyl Quinones

The ready evolution of the adducts into aromatic quinones by spontaneous sulfinyl elimination and further aromatization prompted the use of sulfinyl naphthoquinones as a synthetic equivalent of the unknown compound naph-thynoquinone [103]. For this purpose, sulfinyl quinones represent a convenient synthetic alternative to haloquinones. The highly regioselective course of the Diels-Alder reactions of 2-phenylsulfinyl-1,4-naphthoquinones (as well as their corresponding thioethers and sulfones) unsymmetrically substituted by 

The reaction of sulfinyl naphthoquinones 114a-c with cyclopentadiene afforded mixtures of two exo-sulfinyl adducts (the endo-orientating character of the quinonic system is clearly predominant). Compound exo(c)-115 was the major product in CH2C12 at -20 °C (de ranged between 80 and 90% depending on the dienophile). The 7r-facial selectivity of the process was reversed in the presence of ZnBr2, exo(t) 115 becoming predominant or exclusive [110]. These catalyzed cycloadditions required shorter reaction times and took place with 

Similar results were obtained in reactions of 114a-c with cyclohexadiene. As a consequence of the lower reactivity of this diene, boiling CHC13 was required to achieve complete transformation of the dienophile in the absence of catalysts, which precluded the isolation of the initial adducts exo(c)-116 and exo(t)-ll6, and led directly to desulfinylated compounds 118 and 118 (identical or enantiomers, see above). In ZnBr2 catalyzed cycloadditions, the required reaction conditions are milder, which allows detection of adducts exo(c)-116 and exo(t)-116 by NMR spectroscopy. This revealed that their 7r-facial selectivity was higher than that obtained from cyclopentadiene. 

The stereochemistry of the adduct 113a, obtained as major under thermal conditions, indicates that it is derived from endo-approach to conformation A. It suggests that rotamers with the sulfinyl oxygen in s-cis arrangement (B in Fig. 10) are not the most populated in the conformational equilibrium, even though they are favored upon electrostatic grounds. The higher stability of con- 

Similar results were obtained in reactions of 114a with acyclic dienes bearing oxygenated functions at the allylic stereogenic carbons [117c]. In this case, the 

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TL 27 5509 (1986) (3-sulfinyl-2-aUcenoate ester) 28 107 (1987) (3-sulfinyl-2-alkenoate ester) 30 3853 (2-suiiinyI-2-a]ken-l-oiie)l 4003 (sulfinyl quinone), 4227 (fumaric diamide), 6973 (2-alkoxycarbonyl-2-alkene-4-lactam), 6977 (2-alkoxycarbonyl-2-alkene-4-lactam) (1989) 32 947 (sulfinyl maleate), 2005 (2-acyl-2-alkenoate ester), 7751 (4-aIkoxy-3-sulfonyl-2-alken-4-olide) (1991)... 

JOC 56 1983 (1991) (sulfinyl maleimide) 574664 (2-cyano-2-alkenoate ester), 6870 (sulfinyl quinone) (1992) 59 1499 (sulfinyl maleate), 2211 (l-nitro-2-suIfinyl-l-alkene), 7774 (2-cyano-2-alkenoate ester) (1994) 60 4962 (1995) (1,1-disuMmyl-l-aIkene)... 

Discrepancies between different researchers derive from the character inter-or intramolecular of the interactions presumably controlling the reactive conformation. Thus, in most of the cases, the population of the different rotamers in the sulfinylated substrate (only governed by intramolecular interactions) is the only factor considered for explaining the observed 7r-facial selectivity. This explanation (static conformational polarization) was formulated by Koizumi and used by many authors to justify the behavior of vinyl sulfoxides acting as dienophiles and dipolarophiles. A second explanation assumes that the interactions of the two reagents in the transition states determine a different reactivity of the rotamers around the C-S bond. This intermolecular factor can become the most important one in the control of the 7r-facial selectivity of the cycloadditions, and therefore the tendency expected from conformational stability criteria was not observed in those cases where the most reactive conformation is not the most populated one. This dynamic conformational polarization has been used just to explain some of the results obtained for sulfinyl quinones and sulfinyl dienes (unexplainable with the above model) but it can be applied to many other cases. 

Diaryl Sulfoxides. Optically active diaryl sulfoxides are prepared by reaction of an aryl Grignard with (—)-menthyl (S)-p-toluenesulfinate 2,5-dimethoxyphenyl p-toly 1 sulfoxide (4), a precursor of sulfinyl quinones, and 3-pyridyl p-tolyl sulfoxide (5),... 

Enantiomers (M)- and (P)-helicenebisquinones [32] 93 have been synthesized by high pressure Diels-Alder reaction of homochiral (+)-(2-p-tolylsulfo-nyl)-l,4-benzoquinone (94) in excess with dienes 95 and 96 prepared from the common precursor 97 (Scheme 5.9). The approach is based on the tandem [4 + 2] cycloaddition/pyrolitic sulfoxide elimination as a general one-pot strategy to enantiomerically enriched polycyclic dihydroquinones. Whereas the formation of (M)-helicene is explained by the endo approach of the arylethene toward the less encumbered face of the quinone, the formation of its enantiomeric (P)-form can be the result of an unfavourable interaction between the OMe group of approaching arylethene and the sulfinyl oxygen of 94. 

The asymmetric Diels-Alder cycloadditions of enantiopure (5)-5-(/ -tolylsulfinyl)-1,4-benzoquinones with Dane s diene under thermal and Lewis acid conditions produce tetracyclic quinones after spontaneous elimination of the sulfinyl group.The Diels-Alder reaction of barrelene with o-benzoquinone produces tetracyclo[6.2.2.2 .0 ]tetradeca-9,ll,13-triene-4,5-dione. Under kinetic control, the Diels-Alder cycloaddition of 2,3-dicyano-p-benzoquinone (98) with cyclopentadiene in MeOH produces the single cycloadduct (99) (Scheme 38). ... 

In 2009, a DKR was reported by Carreno s group for the asymmetric synthesis of atropisomeric biaryl[4] and [5]helicene quinones. Therefore, the asymmetric Diels-Alder reaction of a racemic biaryl diene with a chiral sulfinyl... 

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