Facial selective Diels–Alder reactions of (1R,5R)-(+)-3-carbomethoxy-6,6-dimethylbicyclo[3.1.1]hept-3-en2-one. Unusual ketalization–fragmentation reaction of adducts

Abstract

The stereofacially differentiated enone ester 5 has been used to study the effects of steric influence on the Diels-Alder reaction. In general, under Lewis acid catalysis, 5 adds to dienes at low to ambient temperatures in a reasonable rate. Yields of predictable chiral adducts are moderate with the unexpected exception of zinc chloride catalyzed reactions, which provide good to high yields. In all cases only products of addition to the Si face of general type 21 were observed. The regiochemistry of the adducts is exclusively that predicted by the ortho and para rules. The stereochemistry shows a high selectivity in favor of ester-endo transition state products. Rationales for the observed stereoselectivities are discussed. The fragmentation of adducts of 5, in particular keto ester 9, has been briefly examined. Olefins 30 and 46 derived from 9 have been converted to ring-opened cadinane skeletons 31 and 47, respectively, by conditions we have previously reported. In an entirely new and unexpected reaction, simultaneous ketalization and fragmentation of the cyclobutane ring of ketones derived from 9 gave ring-opened ketals 34 + 35 (from 29), 36 + 37 (from 9), 39 (from 38) and 42 + 43 (from 40).HSING-JANG LIU, SEW YEU CHEW, ERIC N.C. BROWNE et JEUNG BEA KIM. Can. J. Chem. 72, 1193Chem. 72, (1994.On a utilisC 1'Cnone ester 5 stCrCofacialement diffCrenciC pour Ctudier les effets stCriques sur la rCaction de Diels-Alder. En gCnCral, dans des conditions de catalyse acide de Lewis, le composC 5 s'additionne aux dibnes a des vitesses raisonnables, des tempkratures ne dCpassant pas la tempkrature ambiante. Les rendements des adduits chiraux attendus sont modCrCs, a l'exception notable des rkactions catalysCes par le chlorure de zinc qui donnent des rendements allant de bons 5 excellents. Dans tous les cas, on n'observe que les produits d'addition sur la face Si, de type gCnCral21. La rtgiochimie des produits est exclusivement celle que l'on peut prCdire sur la base des rbgles ortho etpara. La stCrCochimie prksente une grande sClectivitC pour les produits formCs par le biais de 1'Ctat de transition endo de l'ester. On a examink bribvement la fragmentation des adduits du produit 5, en particulier le cCto ester 9. Utilisant des conditions rapportCes antkrieurement, on a transform6 les olkfines 30 et 46, provenant du produit 9, en squelettes des cadinanes 2 cycle ouvert 31 et 47 respectivement. Par une rCaction aussi nouvelle qu'inattendue, une cktalisation et une fragmentation simultanCe du noyau cyclobutane des cCtones dCrivCs du produit 9 ont fourni les cCtals a cycles ouverts 34 + 35 (ii partir de 29), 36 + 37 (ii partir de 9), 39 (a partir de 38) et 42 + 43 (a partir de 40).[Traduit par la RCdaction]

Face-selective Diels–Alder reactions of (1R,5R)-3-formyl-6,6-dimethylbicyclo[3.1.1]hept-3-en-2-one

“…The resulting 'Osee analytical data and footnote 15 in ref. 11. mixture was stirred for 1.5 h, then water (5 mL) was added and the phases were separated.…”

“…The yield of product 24 was not affected by the reduction in the amount of the diene used. E Addition to 1,3-cyclopentadiene Attempts to induce addition of 1,3-cyclopentadiene to 11 with boron trifluoride etherate as catalyst were unsuccessful due to rapid polymerization of the diene. When zinc chloride was used, the Diels-Alder reaction produced a mixture of two inseparable adducts (20: 1 by 'H nrnr) in 52% yield.…”

α-Activated Cross Conjugated Cycloalkenone Systems in Organic Synthesis

“…The facially differentiated enone ester 29 has been applied to study the effects of steric influence on the Diels-Alder reaction (Scheme 13) [17]. Under catalysis with ZnCl 2 , only products via addition of dienes to the Si face were obtained.…”

ChemInform Abstract: Diels—Alder Reactions of 4,4‐Disubstituted 2‐Cyano‐2,5‐cyclohexadienones. A Facile Approach to the Angularly Substituted cis‐Decalin System.

“…The use of an activating group to enhance the dienophilicity of cyclic enones as a general approach to facilitate the preparation of polycyclic compounds has drawn considerable interest in recent years. 1 A large number of activating groups have been applied, including carbalkoxyl, [2][3][4][5] formyl, [6][7][8] nitro, 9 phenylthio, 10 phenylselenenyl, 11 bromo, 12,13 etc. Placement of an electron withdrawing substituent at the a-position is more common than that at the bposition, although there have been a few examples involving 3-substituted 2-cycloalkenones.…”