Synthese und Hydrolyse von 6-exo-substituierten 2-Methyl-2-exo-norbornyl und 2-Methyl-2-endo-norbornyl-(2,4-dinitrophenyl)äthern Norbornane. 16. Mitteilung

The Synthesis and Hydrolysis of 6-exo-Substituted 2-Methyl-2-exo-norbornyl and 2-Methyl-2-endo-norbornyl 2,4-Dinitrophenyl Ethers The synthesis of the title compounds and their hydrolysis products in aqueous dioxane are described. Upon hydrolysis, the 2-exo-ethers 1 (X=N₂phO) as well as the 2-endo-ethers 2 (X=N₂phO) yield the corresponding 2-methyl-2-exo-norbornanols 3 only. Therefore, the 2-exo-ethers react with retention of configuration at C(2), the 2-endo-ethers 2 with inversion at C(2).     

Inductivity and Bridging in 2-Bicyclo[2.2.2]octyl Cations. Polar Effects,Part 11

The solvolysis rates and products of several 6-substituted 2-exo- and 2-endo-Bicyclo[2.2.2]octyl p-toluenesulfonates, 12 and 13 , respectively, are reported. Inductivity, as measured by the reaction constants ρ_I, is considerably less in the exo-series 12 (ρ_I = ?1.50) than in the corresponding 2-exo-norbornyl p-toluenesulfonates 1 (ρ_I= ?2.0). It is proposed that, for geometrical reasons, bridging of the cationic center C(2) by C(6) is not as strong in the bicyclooctane series 12 as it is in the norbornane series 1 . On the other hand, inductivity is higher in the 2-endo-bicyclooctane series 13 (ρ_I= ?1.0) than in the corresponding 2-endo-norbornane series 3 (ρ_I = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion. The relative yields of exo- and endo-substitution products from the series 12 and 13 , are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations. But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2-endo-bicyclooctane series 13 . Consequently, in the free unsubstituted bicyclooctane cation C(2) is bridged symmetrically by C(6) and C(7), in contrast to the current concept of ‘non-classical’ two-electron-three-center bonding.     

Carbon Participation in the Solvolysis of 6- and 7-Substituted 2-Norbornyl p-Toluenesulfonates. Norbornanes,Part 11

The solvolysis rates and products of several 7-anti-substituted 2-endo-norbornyl p-toluenesulfonates 11 have been determined and compared with those of the previously reported 6-exo-substituted 2-exo-norbornyl p-toluenesulfonates 1. Although the number of bonds between the substituent and the reaction site is the same in the two series, the inductive effect of the substitutents is transmitted far more strongly in the 6-exo-2-exo-series 1 than in the 7-anti-2-endo-series 11 ; i.e. their inductivities differ widely. It is concluded that through space induction involves graded bridging of the substituent-bearing C-atom to the incipient cationic center at C(2) and that this involves differential bridging strain. The different reactivities of unsubstituted 2-exo- and 2-endo-norbornyl derivatives can then be ascribed to a stereoelectronic effect.     

Norbornanes. Part 20. Inductivity and bridging in 2-norbornyl cations

The solvolysis rates and products of several 1-substituted 2exo- and 2-endo-norbornyl p-toluenesulfonates 7 and 8 , respectively, have been determined. Hydrolyses of these epimeric tosylates yielded rearranged products in varying amounts, except when the substituent was COOCH₃ or CN. The logarithms of the rate constants (log k) for the endo-series 8 correlated linearly with the corresponding inductive constants σ with a reaction constant ρ_I of ?1.24. On the other hand, log k values for the exo-series 7 appear to fit two regression lines, the first line (ρ_I = ?1.90) defined by the tosylates that ionize, with rearrangement, to the tertiary cations 11 , the second (ρ_I = ?1.86) by the tosylates 7 (R = H, COOCH³, and CN) that ionize to an asymmetrically bridged secondary cation 19 . These results confirm the unique participation of C(6) with a ρ_I of ?2.00 in the ionization of 2-exo-nor-bornyl tosylate.     

Carbon Participation in the Solvolysis of 6-exo-substituted 2-exo- and 2-endo-Norbornyl p-Toluenesulfonates. Norbornanes part 5

The solvolysis rates and products of the 6-exo-substituted 2-exo- 1a - 1u , and 2-endo-norbornyl p-toluenesulfonates 2a - 2u , have been determined. In general, the rate constants for 1 and 2 (log k) correlate well with the inductive constants σ of the substitutents at C(6); however, their sensitivity to σ is much larger in the 2-exo-series 1 than in the 2-endo-series 2 . This differential transmission of polar effects is the cause of decreasing 2-exo/2-endo rate ratios from 2388 for R = t-C₄H₉ to 0.37 for R = Br, i. e. with increasing electron attraction by the substituent. The high sensitivity of the rate constants for the 2-exo-p-toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)-atom, i. e. to 1,3-bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3-bridging, lead to faster reactions and to the formation of 2-exo substitution products. Conversely, acceptor substituents reduce 1,3-bridging, decrease rates and facilitate the formation of 2-endo substitution products. Graded 1,3-bridging is discussed in the light of Winstein's nonclassical ion concept.     

Stereoselective Synthesis of 2,4,6-Trimethylcyclohex-4-ene-1,3-diol Derivatives and of polypropionate fragments with four contiguous stereogenic centers

The Diels-Alder adduct (±)- 3 of 2,4-dimethylfuran and 1-cyanovinyl acetate was converted stereoselectively into benzyl 6-(4-chlorophenylsulfonyl)-1,3-exo,5-trimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl ( 26 ) and -2-endo-yl ether ( 36 ). Addition of LiAlH₄ to the latter led to the 3-O-benzyl derivatives 28 and 37 of (1RS,2SR,3SR,6SR)- and (1RS,2SR,3RS,6SR)-5-(4-chlorophenylsulfonyl)-2,4,6-trimethylcyclohex-4-ene-1,3-diol, respectively. Methylenation of 6-exo-(4-chlorophenylthio)-1-methyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-one ( 16 ), obtained by reaction of (±)- 3 with 4-Cl-C₆H₄SCl and saponification gave, 6-exo-(4-chlorophenylthio)-1-methyl-3,5-dimethylidene-7-oxabicyclo [2.2.1]heptan-2-one ( 43 ), the reduction of which with K-Selectride afforded 6-exo-(4-chlorophenylthio)-1,3-endo-dimethyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-endo-ol ( 44 ). The 3-O-benzyl derivative 48 of (1RS,2RS,3RS,6SR)-5-(4-chlorophenylsulfonyl)- 2,4,6-trimethylcyclohex-4-ene-1,3-diol was derived from 44 via based-induced oxa-ring opening of benzyl 6-endo-(4-chlorophenylsulfonyl)-1,3-endo-5-endo-trimethyl-7-oxabicyclo[2.2.1]hept-2-endo-yl ether ( 49 ). Benzylation of 28 , followed by reductive desulfonylation and oxidative cleavage of the cyclohexene moiety afforded (2RS,3SR,4RS,5RS)-3,5-bis(benzyloxy)-2,4-dimethyl-6-oxoheptanal ( 32 ).     

The Homoconjugated Electron-Releasing Carbonyl Group of 1-Methylbicyclo[2.2.1]hept-5-en-2-one. Regioselective syntheses of 5-chloro- and 6-chloro-1-methylbicyclo[2.2.1]hept-5-en-2-one

Syntheses of (±)-2-exo-cyano-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate ( 1 ) and of (±)-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 2 ) are reported. The additon of PhSeCl to 1 afforded (±)-5-endo-chloro-2-exo-cyano-1-methyl-6-exo-(phenylselenenyl)-7-oxabicyclo[2.2.1]hept-2-endo-yl acetate ( 6 ), whereas 2 added to PhSeCl with the opposite regioselectivity giving (±)-6-endo-chloro-1-methyl-5-exo-(phenylselenenyl)-7-oxabicyclo[2.2.1]heptan-2-one ( 7 ). These adducts were converted into 5-chloro-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 9 ) and 6-chloro-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 10 ), respectively.     

Norbornanes. Part 18. Inductive Charge Dispersal in the Solvolyses of 4- and 5-Substituted 2-Norbornyl p-Toluenesulfonates

The solvolysis rates and products of 4- and 5-exo-substituted 2-exo- and 2-endo-norbornyl tosylates 9 and 10 , respectively, are reported. The logarithms of the rate constants (log k) correlate linearly with the inductive constants σ for the substituents. A comparison of the reaction constants p₁ for the 4-, 5-, 6-, and 7-substituted 2-exo- and 2-endo-tosylates 9 , 10 , 1 , and 2 respectively, indicates that inductivity is higher for 2-exo-ionization than for 2-endo-ionization in all series. This observation is attributed to the more favorable alignment of neighbouring C-atoms for dorsal participation in exo-ionization, especially, in the case of C(6).     

The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part V. Rearrangements of 1,2-trimethylenenorbornanes initiated by regioselective formation of carbocation centers at C(2) and C(6)

The behaviour of the regioselectively generated carbocation centers at C(2) and C(6) in 1,2-trimethylenenorbornanes was investigated in order to study the occurrence or absence of a degenerate rearrangement E⇄M in the adamantane rearrangement of both 1,2-endo- ( 1 ) and 1,2-exo-trimethylenenorbornane ( 2 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ). A degenerate rearrangement E⇄M is inevitably involved inasmuch as a 1,2-trimethylenenorborn-2-yl cation E not only is formed directly as manifested by the conversions of the reactants 4 (C(2), C(3)-olefin) and 6 (C(2), C(3′)-olefin), but also indirectly (via F→E ) if the leaving group at C(6) to be ionized occupies the endo-position (6-endo-alcohol 8 ). No degenerate rearrangement E⇄M is operative starting from reactants that lead directly to a 2,6-trimethylenenorborn-2-yl cation G ; this is the case with both the ionization of the 6-exo-alcohol 10 having the leaving OH-group in a stereoelectronically favoured configuration to undergo simultaneous C(1), C(2)-bond migration (→ G ) as well as the protonation of the olefin 13 which is followed by same reaction pathway.     

The adamantane rearrangement of 1,2-trimethylenenorbornanes. Part IV. Hydride-ion abstraction in 1,2-exo-trimethylenenorbornane

In the AlBr₃-catalyzed adamantane rearrangement in CS₂ of 1,2-exo-trimethylenenorbornane ( 1 ) to 2-endo,6-endo-trimethylenenorbornane ( 3 ), hydride-ion abstraction occurs at C(6) from the exo-side. The k_H/k_D value for competition between 1 and 5 (D_exo-C(6)) was 1.58 ± 0.05, whereas no kinetic isotope effect was operative for competition between unlabeled 1 and 4 (D_endo-C(5)) and between 1 and 6 (D_endo-C(6)).     

13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols

Carbon chemical shifts and direct ¹³C? ¹H coupling constants of 2-endo-methyl-5-norbornen-2-exo-ol, 2-exo-methyl-5-norbornen-2-endo-ol, 2-endo-methylnorbornan-2-exo-ol and 2-exo-methylnorbornan-2-endo-ol have been measured from single samples using a dual probe pulse Fourier transform method.     

Preparation of 3-bromo-2-methylfuran and 4-bromo-2-methylfuran

4-endo-5-exo-Dibromo-3-methyl-3,6-endo-oxyperhydrophthalic anhydride 3b and 4-exo-5-endo-dibro-mo-3-methyl-3,6-endo-oxyperhydrophtbalic anhydride 3c were isolated from the bromo-adducts of 3-methyl-3,6-endo-oxy-1,2,3,6-tetrahydrophthalic anhydride 2. When 3b or 3c was heated in quinoline, only 3-bromo-2-methylfuran 4 was obtained from 3b and only 4-bromo-2-methylfuran 5 from 3c.     

Zur Konfiguration der 2,4,6,8-Tetrabrom-cyclooctan-1,5-dione Reduktion des β-Isomers durch Natrium-borhydrid

Of the two previously described 2,4,6,8-tetrabromo-cyclooctane-1,5-diones, the higher melting β-isomer, mp. 226°, was treated with sodium borohydride to give: (1) by a double reduction and an intramolecular S_N2-reaction two epimeric alcohols, namely the 2-exo-hydroxy- ( 6 ) and 2-endo-hydroxy- ( 7 ) isomers of 3-exo,5-exo,7-endo-tribromo-9-oxa-bicyclo[4.2.1]nonane, and (2) by a single step reduction a hemiketal, 1-hydroxy-2-exo,4-exo,6-endo,8-endo-tetrabromo-9-oxa-bicyclo[3.3.1]nonane ( 8 ). The structures of these three hydroxy-compounds ( 6, 7 and 8 ) were derived from their properties, especially from complete analyses of their NMR.-spectra, which led to deductions of all configurations and conformations. Of special interest is the preferred existence of the 9-oxa-bicyclo[3.3.1]norane derivative 8 in a chair-chair conformation. The derivation of the configurations of the three hydroxy-compounds 6, 7 and 8 is tantamount to establishing the 2,4-cis, 4,6-trans, 6,8-cis-configuration ( 5 ) of the β-isomer of 2,4,6,8-tetrabromocyclooctane-1,5-dione, mp. 226°.     

Thermal decomposition products of methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates

Methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates at 138°C undergo decomposition via elimination of nitrogen molecule with formation in each case of five products. Two products are methyl 1,3-diphenyl(or 1-methyl-3-phenyl)bicyclo[1.1.0]butane-2-endo- and -exo-carboxylates, and the three others are derivatives of buta-1,3-diene, methyl (Z)-2-benzylidene-3-phenyl(or 3-methyl)but-3-enoate and methyl (E)- and (Z)-3,4-diphenyl(or 4-methyl-3-phenyl)penta-2,4-dienoates. The formation of these products may be rationalized assuming intermediacy of substituted allylcarbene which undergoes both intramolecular cycloaddition and rearrangements involving 1,2-hydride and 1,2-vinyl shifts.     

The Diels-Alder Reactivity of 2,2′-Ethylidenebis[3,5-dimethylfuran] and Exploratory Chemistry of the Mono-adducts

In the presence of Me₃Al, 1-cyanovinyl acetate added to 2,2′-ethylidenebis[3,5-dimethylfuran] ( 1 ) to give a 20:10:1:1 mixture of mono-adducts 4,5,6 , and 7 resulting from the same regiocontrol (‘para’ orienting effect of the 5-methyl substituent in 1 ). The additions of a second equiv. of dienophile to 4–7 were very slow reactions. The major mono-adducts 4 (solid) and 5 (liquid) have 2-exo-carbonitrile groups. The molecular structure of 4 (1RS,1′RS,2SR,4SR)-2-exo-cyano-4-[1-(3,5-dimethylfuran-2-yl)ethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate) was determined by X-ray single-crystal radiocrystallography. Mono-adducts 4 and 5 were saponified into the corresponding 7-oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1RS,1′SR,4RS,5RS,6RS)-4-[1-(3,5-dimethyl furan-2-yl)ethyl]-6-exo-methoxy-1,5-endo-dimethyl-7-oxabicyclo [2.2.1]heptan-2-one dimethyl acetal ( 12 ) and its (1′RS-stereoisomer 12a , respectively. Acetal hydrolysis of 12a followed by treatment with (t-Bu)Me₂SiOSO₂CF₃ led to silylation and pinacol rearrangement with the formation of (1RS,1′RS,5RS,6RS)-4-[(tert-butyl)dimethy lsilyloxy]-1-(3,5-dimethylfuran-2-yl)ethyl]-5-methoxy-6-methyl-3-methylidene- 2-oxabicyclo[2.2.1]heptane ( 16 ). In the presence of Me₃Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1RS,1′RS,2″RS,3″RS,4SR,4″RS,5 SR,6SR)-dimethyl 5-exo-hydroxy-4,6-endo-dimethyl-1-[1-(3-exo,5,5-trimeth oxy-2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-2-yl)ethyl]-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate ( 20 ). Acetylation of alcohol 20 followed by C?C bond cleavage afforded (1′RS,1″SR,2RS,2′″SR,3RS, 3″SR,4RS,4″SR,5RS)-dimethyl {3-acetoxy-2,3,4,5-tetrahydro-2,4-dimethyl-5-[1-(3-exo,5,5-trimethoxy ?2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-1-yl)-ethyl]furan-2,5-diyl} bis[glyoxylate] ( 24 ).     

Solvolysen von 4-Alkylidenbicyclo[3.2.0]hept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven

Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF₃SO₂)₂O in CH₂Cl₂/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained.     

Reductive Radical Cyclisations of Bromo Acetals and (Bromomethyl)silyl Ethers of Terpenoid Alcohols

The tin hydride promoted and the reductive vitamin B₁₂ catalysed radical cyclisation of mixed 2-bromo-acetaldehyde acetals and of (2-bromomethyl)dimethylsilyl ethers of allylic terpenoid alcohols has been investigated: 3-oxadeca-5,9-dien-l-yl radicals undergo 5-‘exo’ cyclisation to oxolanes (Scheme 4), 3-oxa-2-siladeca-5,9-dien-1-yl radicals sequential 6-‘endo’→5-‘exo’ tandem cyclisation to cis-3-oxa-4-silabicyclo[4.3.0]nonanes (Scheme 5), and 3-oxa-2-silatetradeca-5,9,13-trien-l-yl radicals sequential 6-‘endo’→6-‘endo’→5-‘exo’ triple cyclisation to trans-transoid-trans- 12-oxa-11-silatricyclo[7.4.0.0^2,6] tridecanes (Scheme 6).     

Norbornanes. Part 19. The Inductive Model for Norbornyl Cation Formation

Two CH₃ groups at C(6) of 2-exo- ( 10a ) and 2-endo-norbornyl p-toluenesulfonate 11a lower their solvolysis rates in 80% EtOH by factors of 28 and 16, respectively. A spirocyclopropyl group including C(6), as in 21a and 22a , reduces the rate of exo- and endo-ionization by factors of 250 and 8, respectively. The geminally dimethyl-substituted tosylates 10a and 11a yield the 2-exo-alcohol 10b , whereas the spirocyclopropyl-substituted tosylates 21a and 22a furnish rearranged 3-brendanol 23 . These findings are readily rationalized by the inductive model, according to which norbornyl cation formation is controlled by the inductive effect of dorsal substituents.     

Synthesis of (+)-1,3:2,5-dianhydroviburnitol ((+)-(1R,2R,3S,5R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol)

Epoxidation of (?)-(1R,2R,4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl acetate ((?)-5) followed by saponification afforded (+)-(1R,4R,5R,6R)-5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7). Reduction of (+)-7 with diisobutylaluminium hydride (DIBAH) gave (+)-1,3:2,5-dianhydroviburnitol ( = (+)-(1R,2R,3S,4R,6S)-4,7-dioxatricyclo[3.2.1.0^3,6]octan-2-ol; (+)-3). Hydride reductions of (±)-7 were less exo-face selective than reductions of bicyclo[2.2.1]heptan-2-one and its derivatives with NaBH₄, AlH₃, and LiAlH₄ probably because of smaller steric hindrance to endo-face hydride attack when C(5) and C(6) of the bicyclo-[2.2.1]heptan-2-one are part of an exo oxirane ring.     

Acid-Catalyzed Rearrangements of 5,6-exo-Epoxy-7-oxabicyclo[2.2.1]hept-2-yl Derivatives. Migratory Aptitudes of Acyl vs. Alkyl Groups in Wagner-Meerwein Transpositions

In the presence of HSO₃F/Ac₂O in CH₂CL₂, 2-exo- and 2-endo-cyano-5,6-exo-epoxy-7-oxabicyclo[2.2.1]hept-2-yl acetates ( 6a , b ) gave products derived from the epoxide-ring opening and a 1,2-shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ( 6c ) gave 5-oxo-2-oxabicyclo[2.2.1]heptane-3,7-diyl diacetates 20 and 21 arising from the 1,2-shift of the acyl group. Acid treatment of 5,6-exo-epoxy-2,2-dimethoxy-7-oxabicyclo[2.2.1]heptane ( 6d ) and of 5,6-exo-epoxy-2,2-bis(benzyloxy)-7-oxabicyclo[2.2.1]heptane ( 6e ) gave minor products arising from epoxide-ring opening and the 1,2-shift of σ bond C(3)–C(4) and major products ( 25 , 29 ) arising from the 1,3-shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6-exo-epoxy-2,2-ethylenedioxy-7-oxabicyclo[2.2.1]heptane ( 6f ) gave 1,1-(ethylenedioxy)-2-(2-furyl)ethyl acetate ( 32 , major) and a minor product 33 , arising from the 1,2-shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2-shifts toward electron-deficient centers has been established: acyl > alkyl > alkyl α-substituted with inductive electron-withdrawing groups. This order is valid for competitive Wagner-Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.