Crystal Structure of Tricarbonyl-[2,3-η:O-σ-(7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1]hept-2-ene)]iron

The product of the reaction of [Fe(benzalacetone)(CO)₃] with 7,7-dimethoxy-5,6-dimethylidenebicyclo[2.2.1] hept-2-ene is tricarbonyl-[2,3-η:O-σ-(7,7-dimethoxy-5,6-dimethylidenebicyclo [2.2.1]hept-2-ene)]iron. Crystals are monoclinic, space group P2¹/c with a = 6.612(2), b = 11.610(4), c = 18.604(6) Å, and β = 95.91(2)°. The coordination at the metal atom is trigonal bipyramidal. The equatorial sites are occupied by 2 CO's and by the midpoint of the endocyclic double bond of the organic ligand. The axial sites are occupied by one CO group and the O-atom of one MeO group of the C(OMe)₂ bridge. It is an uncommon example of a d⁸ metal carbonyl complex bearing an O-bonded ligand.     

Cyclodimerization of 1-(Dimethoxyniethyl)-5,6-dimethylidene-7-oxa-bicyclo[2.2.1]hept-2-ene Induced by Nonacarbonyldiiron. Crystal Structure of (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)- Tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl)-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)]iron

The transition-metal-carbonyl-induced cyclodimerization of 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene is strongly affected by substitution at C(1) While 5,6-dimethylidene-7-oxabicyclo[2.2.1]hept–2-ene-l-methanol ( 7 ) refused to undergo [4 + 2]-cyclodimerization in the presence of [Fe₂(CO)⁹] in MeOH, 1-(dimethoxymethyl)-5,6-di-methylidene-7-oxabicyclo[2.2.1]hept-2-ene ( 8 ) led to the formation of a 1.7:1 mixture of ‘trans’ ( 19, 21, 22 ) vs. ‘cis’ ( 20, 23, 24 ) products of cyclodimerization together with tricarbonyl[C, 5,6, C-η-(l-(dimethoxymethyl)-5,6-di-methylidenecyclohexa-1,3-diene)]iron ( 25 ) and tricarbonyl[C,3,4, C-η-(methyl 5-(dimethoxymethyl)-3,4-di-methylidenecyclohexa-1,5-diene-l-carboxylate)]iron ( 26 ). The structures of products 19 and of its exo ( 21 ) and endo ( 22 ) [Fe(CO)₃(1,3-diene)]complexes) and 20 (and of its exo ( 23 ) and endo (24) (Fe(CO)₃(1,3-diene)complexes) were confirmed by X-ray diffraction studies of crystalline (1RS, 2SR, 3RS, 4RS, 4aRS, 9aSR)-tricarbonyl[C, 2,3, C-η-(1,4-epoxy-1,5-bis(dimethoxymethyl])-2,3-dimethylidene-1,2,3,4,4a,9,9a,10-octahydroanthracene)iron ( 21 ). In the latter, the Fe(CO)₃(1,3-diene) moiety deviates significantly from the usual local C_s symmetry. Complex 21 corresponds to a ‘frozen equilibrium’ of rotamers with η-alkyl, η³-allyl bonding mode due to the acetal unit at the bridgehead centre C(1).     

Chiral exo-Alkylidenecyclopentanes from (1S,4R)-7,7-Dimethyl-1-vinylbicyclo[2.2.1]heptan-2-one

(1S,4R)-7,7-Dimethyl-1-vinylbicyclo[2.2.1]heptan-2-one oxime in the system (CF₃CO)₂O-CF₃COOH and (1S,4R)-1-(1,2-dibromoethyl)-7,7-dimethylbicyclo[2.2.1]heptan-2-one in the system MeONa-MeOH undergo fragmentation to give exo-alkylidenecyclopentane derivatives, (4R)-4-cyanomethyl-5,5-dimethyl-1-[(1E)-trifluoroacetoxyethylidene]cyclopentane and isomeric (4R)-4-carboxymethyl-1-[(1ZE)-2-methoxyethylidene]-5,5-dimethylcyclopentanes, respectively. The trifluoroacetate derivative undergoes unusual rearrangement, yielding an equilibrium mixture of two isomers with endo- and exocyclic double bond.     

The Carbonyl Group as Homoconjugated Electron-Releasing Substituent. Regioselective electrophilic additions at bicyclo[2.2.1]hept-5-en-2-one,bicyclo[2.2.2]oct-5-en-2-one,and derivatives

In CHCl₃, CH₃CN, or AcOH, benzeneselenenyl chloride (PhSeCl), bromide (PhSeBr), and acetate (PhSeOAc), 2-nitrobenzenesulfenyl chloride (NO₂C₆H₄SCl), and 2,4-dinitrobenzenesulfenyl chloride ((NO₂)₂C₆H₃SCl) added to bicyclo[2.2.1]hept-5-en-2-one ( 5 ) in an. anti fashion with complete stereo- and regioselectivity, giving adducts 20–24 in which the chloride, bromide, or acetoxy substituent (X) occupies the endo position at C(6) and the Se- or S-substituent (E) the exo position at C(5), The addition 5 + (NO₂)₂C₆H₃SCl→ 24 was accompanied by the formation of (1RS, 2RS)-2-(2,4-dinitrophenylthio)cyclopent-3-ene-l-acetic acid ( 25 ). The latter was the major product in AcOH containing LiClO₄. The additions of PhSeCl and PhSeBr to bicyclo[2.2.2]oct-5-en-2-one ( 6 ) were less stereoselective (proportion of exo vs. endo mode of electrophilic attack was ca. 3:1) but highly regioselective gazing adducts 27/28 and 29/30 , respectively, the regioselectivity being the same as that of the electrophilic additions of 5 . The reaction of PhSeCl with a 4:1 mixture of 2-exo-chloro- and 2-endo-chlorobicyclo[2.2.1]hept-5-ene-2-carbonitriles ( 12 ) was slower than addition 5 + PhSeCl; it gave adducts 31/32 (4:1) in which the PhSe moiety occupies the exo position at C(6) and the Cl atom the endo position at C(5). The addition of PhSeCl to 2-chlorobicyclo[2.2.1]oct-5-ene-2-carbonitriles ( 13 ) was very slow and gave adducts with the same regioselectivity as 12 + PhSeCl, but opposite with that of reactions of the corresponding enones 5 and 6 . PhSeX (X = Cl, Br, OAc) added to 2-cyanobicyclo[2.2.1]hept-5-en-2-yl acetates ( 14 ) with the same regioselectivity as 12 + PhSeCl. The additions of PhSeCl, PhSeBr, NO₂C₆H₄SCl, and (NO₂)₂C₆H₃SCl to 2-(bicyclo[2.2.1]hept-5-en-2-ylidene)propanedinitrile ( 49 ) were not regioselective, showing that a dicyanomethylidene function is not like a carbonyl function when homoconjugated with a π system. The results are in agreement with predictions based on MO calculations suggesting that a carbonyl group homoconjugated with an electron-deficient centre can behave as an electron-donating, remote substituent because of favourable n(CO)?σC(1), C(2)?p(C(6) hyperconjugative interaction.     

Inductive and Polarizability Effects of an Exocyclic Diene-Iron Tricarbonyl Group. The acetolyses of exo- and endo-irontricarbonyl complexes of 5,6-dimethylidene-2-exo-norbornyl and 2,3-dimethylidene-7-anti-norbornyl parabromobenzenesulfonates

The exo- and endo-irontricarbonyl complexes of 5,6-dimethylidene-2-exo-norbornyl alcohols 10x, 10n , p-bromobenzenesulfonates 11x, 11n , acetate 12x and of the 2,3-dimethylidene-7-anti-norbornyl alcohols 17x, 17n , p-bromobenzenesulfonates 19x, 19n and acetates 20x, 20n have been prepared. The S_N1 buffered acetolyses of 11x, 19x and 19n gave 12x, 20x and 20n , respectively (retention of configuration). The first-order rate constants of the acetolyses have been evaluated and compared with those of the acetolyses of the uncomplexed 5,6-dimethylidene-2-exo-norbornyl ( 14 ) and 2,3-dimethylidene-7-anti-norbornyl p-bromobenzenesulfonates ( 18 ). A rate retardation effect of ca. 1.5 · 10⁵ was measured for 11x → 12x (65°) compared with the acetolysis of 14 . The retardation effect is larger (> 5 · 10⁷) with 11n . Contrastingly, the acetolysis 19x → 20x was slightly accelerated with respect to that of the uncomplexed p-bromobenzenesulfonate 18 . An unsignificant rate-retardation effect was measured for the acetolysis 19n → 20n . The results are interpreted in terms of competitive inductive destabilization and charge-induced dipole stabilizing interaction by the exocyclic diene-iron tricarbonyl fragment. PMO. arguments give a rationale for the difference in polarizability between the diene-Fe(CO)₃ group in 19 and that in the endo-7-norbornadienyl-iron tricarbonyl system.     

Chemo- and Stereoselective Coordination of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene by d8- and d6-Metal Carbonyls. Diels-Alder reactivity of Dienes Perturbed by Remote Olefin Complexation

The endocyclic double bond C(2), C(3) in 5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene ( 1 ) can he coordinated selectively on its exo-face before complexation of the exocyclic s-cis-butadiene moiety. Irradiation of Ru₃(CO)₁₂ or Os₃(CO)₁₂ in the presence of 1 gave tetracarbonyl [(1R,2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]-hept-2-ene)]ruthenium ( 6 ) or -osmium ( 8 ). Similarly, irradiation of Cr(CO)₆ or W(CO)₆ in the presence of 1 gave pentacarbonyl[(1R, 2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]chromium (10) or -tungsten (11) . Irradiation of complexes 6 and 11 in the presence of 1 led to further CO substitution giving bed-tricarbonyl-ae-bis[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene)]ruthenium ( 7 ) and trans-tetracarbonyl[(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo-[2.2.1]hept-2-ene)]tungsten (12) , respectively. The diosmacyclobutane derivative cis-m?-[(1R,3R,3S,4S)-(5,6-dimethylidene-7-oxabicyclo[2.2.1]hepta-2,3-diyl)]bis(tetracarbonyl-osmium) (Os-Os) (9) wa also obtained. The Diels-Alder reactivity of the exocyclic s-cis-butadiene moiety in complexs 7 and 8 was found to be significantly higher than that of the free triene 1 .     

Synthesis and properties of 7,7-dichloro-3,4-benzobicyclo[4.1.0]heptane, its tricarbonylchromium complexes, and isomeric 7-chloro-3,4-benzobicyclo[4.1.0]heptanes

The reaction of Cr(CO)₆ with 7,7-dichloro-3,4-benzobicyclo[4.1.0]heptane gave the correspondingexo- andendo-chromium tricarbonyl complexes in a ratio of 4.5:1. The structures of the resulting compounds were established by NMR spectroscopy, mass spectrometry, and X-ray structural analysis. Reduction of dichlorobenzobicycloheptane and its chromium tricarbonyl complexes with LiAlH₄ affordedexo- andendo-7-chloro-3,4-benzobicyclo[4.1.0]heptanes in a 3.5:1 ratio. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 720–724, April, 1998.     

Sterical Hindrances as a Driving Force of Skeleton Rearrangements of Fenchone and Its Oxime in Ritter Reaction

Fenchone (1,3,3-trimethylbicyclo[2.2.1]heptan-2-one) in reaction with acetonitrile in the presence of sulfuric acid (Ritter reaction) due to steric hindrances preventing geminal addition of two nucleophile molecules gives rise to a mixture of 1,2-exo-diacetamido-6-endo,7,7-trimethylbicyclo[2.2.1]heptane, 2-endo6-exo-diacetamido-3,3,6-trimethylbicyclo[2.2.1]heptane, and 2-exo,6-exo-diacetamido-1,3,3-tri- methylbicyclo[2.2.1]heptane in the ratio of 6:4:1. Fenchone oxime under condition of this reaction affords a mixture of stereoisomeric cis- and trans-acetamido-1-methyl-3-(-cyanoisopropyl)cyclopentanes in 2:3 ratio.     

Circular Dichroism of Planar,Exocyclic S-cis-Butadienes Remotely Perturbed

Optically pure 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl derivatives have been prepared. The sign of the Cotton effects associated with lowest-energy transition of 2–(dicyanomethylidene)-((?)-(1S,4S)- 15 ), (E)-2-(methoxyimino)-((+)-(1S,4S)- 16 ), (Z)-2-(methoxyimino)-5,6-dimethylidenebicyclo[2.2.1]heptane ((?)(1S,4S)- 17 ), and 2,3,5-trimethylidenebicyclo[2.2.1]heptane ((?)-(1R,4S)- 18 ) is opposite to the chirality constituted by the coupling of the electric transition moments of the two homoconjugated π-chromophores (Kuhn-Kirkwood dipole-coupling mechanism). When the substituents at C(2) are not π-functions, no general rule can be retained for the chiroptical properties of the 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl systems as shown for dimethyl acetal (?)-(1S,4S)- 19 , ethylene acetal (+)-(1R,4R)- 20 , exo and endo methyl ethers (+)-(1R,2S,4R)- 21 and (+)-(1R,2R,4R)- 22 , and for spirol[5,6-dimethylidenebicyclo[2.2.1]heptane-2.2'-oxiranes](?)-(1S,2S,4S)- 23 and (?)-(1S,2S,4S)- 24 .     

RATES OF RING-OPENING OF 2,2,4,7,7-PENTAMETHYL-3,6-DITHIAOCTANE TETRACARBONYL TUNGSTEN (0)

Abstract

Ring displacement from η²-PDOW(CO)₄ (PDO = 2,2,4,7,7-pentamethyl-3.6-dithiaoctane) by L (L = P(0-i-Pr)₃ and P(OEt)₃) produces a mixture of cis- and trans- (L)₂W(CO)₄. Results from kinetics experiments are consistent with the results observed for the structurally-related η²-DTOW(CO)₄ complex (DTO = 2,2,7,7-tetramethyl-3,6-dithiaoc-tane). A smaller value for the rate constant (k₁) for the ring-opening step of η²-PDOW(CO)₄ reflects the shorter W-S bond distances observed in η²-PDOW(CO)₄. This observation is consistent with the trend observed for a series of η²-DTAW(CO)₄ complexes (DTA = Dithiaalkanes) in which the value of k₁ increases with the size of the chelate ring. Since the species η²-PDOW(CO)₄ and η²-DTOW(CO)₄ are five-membered chelate complexes, differences in their molecular and kinetic parameters are being ascribed to the methyl group in the chelate backbone of η²-PDOW(CO)₄. Our observations confirm earlier findings that small differences in the structure of DTA greatly affect the rates of ring-opening in η²-DTAW(CO)₄ complexes.     

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.     

A thermal route to stereospecifically CO labelled group VIB metal pentacarbonyl amine derivatives

A method for the synthesis of stereospecifically, equatorially labelled cis-M(CO)₄(¹³CO)(amine) derivatives where M = Cr, Mo, and W has been developed involves ¹³CO substitution into the vacant coordination site created by the facile dissociation of an amine ligand from cis-M(CO)₄(amine)₂ derivatives. The mechanistic implications of this extremely stereoselective reaction are discussed.     

Direct ionic chlorination of alkyl sulfones with sulfuryl chloride

The introduction of a Cl atom usually takes place at a position a to the α atom of alkyl sulfones. In this paper, a new ionic chlorination method of alkyl sulfones with sulfuryl chloride in which the most noteworthy observation was exclusive or highly selective β-chlorination of diethyl sulfone or sulfolane (tetrahydrothiophene-1,1-dioxide) is described. The most successful synthetic application of this method was exemplified by the chlorination of 7-thiabicyclo[2.2.1]heptane-7,7-dioxide, which affords 2-exo- and 2-endo-chloro-7-thiabicyclo[2.2.1]heptane-7,7-dioxides, which were difficult to obtain by the radical chlorination, probably because of the undesired homolytic SO₂C bond fission. 2-exo-Chloro-7-thiabicyclo[2.2.1]heptane-7,7-dioxide, thus obtained, was selectively reduced to give 2-exo-chloro-7-thiabicyclo[2.2.1]heptane. A mechanism for this chlorination is also discussed.     

Iron carbonyl complexes of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane. Crystal and molecular structure of (C10H10O)Fe(CO)3 and (C9H10CO)Fe2(CO)6

The reaction of 2,3,5,6-tetrakis(methylene)-7-oxabicyclo[2.2.1]heptane (I) with iron carbonyls in various solvents yields the (η⁴-1,3-diene)Fe(CO)₃ isomers (II: exo; III: endo) and the bimetallic isomers bis[(η⁴-1,3-diene)Fe(CO)₃] (IV: bis(exo); V: endo,exo). In weakly coordinating solvents, a parallel rearrangement of I occurs through CO bond cleavage of the allylic ether by Fe₂(CO)₉ yielding an unsaturated ketone (VI) bonded to two Fe(CO)₃ groups through a trimethylenemethane and a 1,3-diene system, respectively. The geometries of III and VI have been ascertained by X-ray crystal structure determinations.     

Indenyl and fluorenyl transition metal complexes : VII. Innersphere “ricochet” rearrangements on alkylation of η5-indenyl- and η5-fluorenyltricarbonylchromate anions

Alkylation of K[η⁵-C₉H₇Cr(CO)₃] (Xa) with CH₃I and C₆H₅CH₂Br leads to σ-alkyl derivatives of η⁵-C₉H₇Cr(CO)₃Alk type. These complexes undergo innersphere “ricochet” rearrangement, with the alkyl group being shifted to the endo position at C(1) and the chromium tricarbonyl group shifted to the benzene nucleus. The structure of the product of such a rearrangement in the case of η⁵-C₉H₇(CO)₃CrCH₂C₆H₅, i.e. (1-benzyl-3a,4-7,7a-η⁶-indene)chromium tricarbonyl (XVIII), is established by a low temperature X-ray study, indicating an endo position for the benzyl radical.On alkylation of equilibrium tautomeric mixtures of η⁵- and η⁶-fluorenylchromium tricarbonyl anions XIa ? XIb under similar conditions, the η⁵-anion (Xa) yields a σ-alkyl derivative, which is rearranged to (9-endo-alkyl-1-4,4a,9a-η⁶-fluorene)chromium tricarbonyl. Electrophilic attack of the η⁶-anion (XIb) takes place on the outer side at C(9) and leads to a corresponding 9-exo-alkyl derivative.     

Synthese,Kristallstrukturen und Eigenschaften von Lanthanoid(III)-Komplexen mit 7-Oxa-bicyclo[2.2.1]heptan-2,3-dicarbonsäure

Synthesis, Crystal Structures, and Properties of Lanthanoid(III) Complexes with 7-Oxa-bicyclo[2.2.1]heptane-2,3-dicarboxylic Acid The synthesis of coordination compounds [ML(HL)(H₂O)] with M = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺ and H₂L = 7-oxa-bicyclo[2.2.1]heptane-2-exo,3-cis-dicarboxylic acid ( 1 ) has been described. Results of IR spectroscopy and thermal decomposition are given. As a result of X-ray analyses, the four investigated lanthanoid(III) complexes are isotypic. Their stereochemistry approximates to the tri-capped trigonal prism with nine O atoms coordinating the metal atom. The bicyclic ligand acts as a tridentate chelating monoanion HL^? as well as a pentadentate dianion L^2? with both chelating and bridging function. One coordination place at the metal atom is occupied by a water molecule.     

(η3-allyl)palladium(II) catalysts for the addition polymerization of norbornene derivatives with functional groups

Cycloaliphatic polyolefins with functional groups were prepared by the Pd(II)-catalyzed addition polymerization of norbornene derivatives. Homo- and copolymers containing repeating units based on bicyclo[2.2.1] hept-5-en-2-ylmethyl decanoate (endo/exo-ratio = 80/20), bicyclo[2.2.1]hept-5-ene-2-carboxylic acid methyl ester (exo/endo = 80/20), bicyclo[2.2.1]hept-5-ene-2-methanol (endo/exo = 80/20), and bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (100% endo) were prepared in 49–99% yields with {(η³-allyl)Pd(BF₄)} and {(η³-allyl)Pd(SbF₆)} as catalysts. The catalyst containing the hexafluoroantimonate ion was slightly more active than the tetrafluoroborate based Pd-complex.     

Interaction between Exocyclic s-cis-Butadiene and Homoconjugated Functions. Preparation and Diels-Alder Reactivity of Remotely Substituted 2,3-Dimethylidenebicyclo[2.2.2]octanes

The preparations of 5,6-dimethylidene-2exo-bicyclo[2.2.2]octanol ( 8 ), its endo isomer 9 , 5,6-dimethylidene-2-bicyclo[2.2.2]octanone ( 10 ) and 2 exo, 3 exo-epoxy-5,6dimethylidenebicyclo[2.2.2]octane ( 11 ) are described. The kinetics of their cycloaddition to tetracyanoethylene has been measured in toluene at 25° together with those of 2,3-dimethylidenebicyclo[2.2.2]octane ( 7 ) and 5,6-dimethylidenebicyclo[2.2.2]oct-2-ene (12). The effects of remote substitution on the Diels-Alder reactivity of 2,3-dimethyl idenebicyclo[2.2.2]octanes are compared with those observed in the 2,3-dimethylidenenorbornane series ( 1–6 ).     

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.     

Reaktionen mit phosphororganischen Verbindungen, 49. Synthese und 1H-NMR-Spektren von (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonsäureestern

Reactions with Organophosphorus Compounds, 49. Synthesis and ¹H NMR Spectra of (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonates Reaction of the (E)-(β-acylvinyl)phosphonates 1 with cyclopentadiene yields the isomeric norbornylphosphonates 2 (endo-acyl, exo-P) and 3 (exo-acyl, endo-P) in a 7:3 ratio. With 1,3-cyclohexadiene the corresponding bicyclooctenyl derivatives 7 and 8 are obtained from 1a . The (Z)-phosphinylacrylate 4 gives with cyclopentadiene the isomers 5 (exo-CO₂Me, exo-P) and 6 (endo-CO₂Me, endo-P) in nearly equal amounts. The configuration of the cycloadducts has been proved by ¹H NMR spectroscopy.