Effect of substituents in the cumulene and aryl fragments of aroylketenes on the stereoselectivity of diels-alder heteroreaction with mono-, Bi-, and polycyclic terpenoids containing a carbonyl group

Abstract

Keywords: aroylketenes, (R)-, (S)-spiro-1,3-dioxin-4-ones, terpenoids, (4+2) cycloaddition.Substituted furan-2,3-diones react with aldehydes and ketones with the formation of substituted 6-aryl-1,3-dioxin-4-ones [1,2], displaying biological activity [3]. Continuing these studies we have investigated the effect of substituents in furandiones on the course of the reaction with optically active l-menthone, camphor, and allobetulone.As a result of the interaction of 5-arylfuran-2,3-diones 1a,b with menthone we obtained a mixture of approximately equal quantities of the stereoisomeric adducts spiro[(6-aryl-3,4-dihydro-2H-1,3-dioxin)-2,2'-(1-isopropyl-4-methylcyclohexan)]-4-ones 3a,b and 4a,b. According to data of 1 H NMR spectroscopy, compounds 3 and 4 exist as a mixture of diastereoisomers with (R)-and (S)-configurations of the spiro carbon atom. O O O R O O R O O O O R O O O R 1a,b 2a,b 3a,b 4a,b -CO  1-4 a R = H, b R = Me

Allobetulin and Its Derivatives: Synthesis and Biological Activity

“…The two isomers 19a,b were isolated and characterized by X-ray crystallography [ 38 ]. The effect of the substituents on the cumulene and aryl fragments on the stereoselectivity was studied [ 39 ].…”

“…[ 62 ] Dehydrobromination of 28 or 29 gave unsaturated ketones 30a,b [ 55 , 59 ]. Ketone 30a (R = H) was also prepared directly via phenylselenic anhydride oxidation of allobetulone 4 [ 39 ] and was used as a Michael acceptor for cyanide anion ( Figure 7 ) [ 41 ].…”

Acyl(imidoyl)ketenes: Reactive Bidentate Oxa/Aza-Dienes for Organic Synthesis

“…However, a similar reaction of ketenes A8 with camphor does not produce desired derivatives 21 nor derivatives J, and instead products of dimerization of acyl(imidoyl)ketenes A8 to compounds 13.3 are observed [68]. Such a change in regioselectivity of the reaction may be caused by steric difficulties created by the three methyl groups in camphor [68].…”

“…The reaction proceeds regioselectively, and formation of alternative products, [1,3]oxazino [3,4-a]quinoxalin-3-ones J, is not observed (Scheme 18). The reaction of acyl(imidoyl)ketenes A8 with allobetulone proceeds in a similar way to result in corresponding derivatives 21 (Scheme 18) [68]. However, a similar reaction of ketenes A8 with camphor does not produce desired derivatives 21 nor derivatives J, and instead products of dimerization of acyl(imidoyl)ketenes A8 to compounds 13.3 are observed [68].…”

“…Acyl(imidoyl)ketenes A8 generated from (quinoxalin-2-yl)furan-2,3-diones 3 react with carbonyl compounds 20 (aldehydes and ketones) to form exclusively 5-(quinoxalin-2yl)-4H-1,3-dioxin-4-ones 21 (Scheme 18) [68,69]. Trapping reagents 20 are added directly to the reaction mixture before heating.…”