Face Selectivity of the Diels-Alder Additions of 2-Substituted 5,6-bis((E)-chloromethylidene)bicyclo[2.2.2]octanes

The preparation of 5,6-bis((E)-chlorommethylidene)bicyclo[2.2.2]oct-2-ene ( 13 ), 2,3-bis((E)-chloromethyl idene)-5exo,6exo- and -5endo,6endo-epoxybicyclo[2.2.2] octane ( 14 and 15 ), 5,6-bis((E)-chloromethylidene)-2exo- and -2endo-bicyclo[2.2.2] octanol ( 16 and 17 ) and 5,6-bis((E)-chloromethylidene)-2-bicyclo[2.2.2]octanone ( 18 ) are described. The face selectivity (endo-face vs. exo-face attack onto the exo-cyclic diene) of their cycloadditions to tetracyanoethylene has been determined in benzene at 20°. It is 78/22, 80/20, 60/40, 68/32, 3/97 and 30/70 for 13 , 14 , 15 , 16 , 17 and 18 , respectively.     

The 7,8-epoxy-2,3,5,6-tetrakis(methylene) bicyclo[2.2.2]octane; synthesis and diels-alder reactivity

The preparation of 7,8-epoxy-2,3,5,6-tetrakis(methylene)bicyclo[2,2,2] octane (5) is described. Evidence for transannular interaction between the homoconjugated s-cis-butadiene functions in 5 is found in the UV absorption spectrum. The Diels-Alder addition of 5 to tetracyanoethylene (TCE) is syn-regioselective and leads to the monoaducts 16:17 (85:15). The dienes 16,17 are less reactive than 5 toward TCE. anti-regioselectivity (leading to exo-2, endo-3-bis(chloromethyl)-5,6-bis(methylene)-syn-7,8-epoxybicyclo[2.2.2]octaves (25) is observed in the double elimination of HCl from the syn-7,8-epoxy-exo-2,endo-3,exo-5,endo-6-tetrakis(chloromethyl)bicyclo[2.2.2]octane (11), precursor of 5. The structures of the regioisomers 16,17 were confirmed spectroscopically and chemically. Elimination of HCl from the chloromethyl groups in 26 (TCE adduct of 25) and HCN from the TCE adducts 16, 17 and 26 can be induced by CsF in DMF.     

Face Selectivity of the Diels-Alder Additions of Exocyclic Dienes Grafted onto 7-Oxabicyclo[2.2.1]heptanes

Stereoselective syntheses of 2exo, 3exo-bis (chloromethyl)-5-[(Z)-chloromethylidene]- ( 9 ), 2exo, 3exo-bis (chloromethyl)5-[(E)-chloromethylidene]- ( 10 ) and 2exo, 3exo-bis(chloromethyl)-5-[(E)-methoxymethylidene]-6-niethylidene-7-oxa-bicyclo[2.2.1]heptane ( 13 ) are presented. Double elimination of HCI from 9, 10 and 13 yielded 2-[(Z)-chloromethylidene]- ( 14 ), 2-[(E)chloromethylidene]- ( 15 ) and 2-[(E)-methoxymethylidene]-3,5,6-mmethylidene-7-oxabicycio[2.2.1]heptane ( 18 ), respectively, without loss of the olefin configuration. Ethylene tetracarbonitrile (TCE) and N-phenyltriazolinedione (NPTAD) added to these new exocyclic dienes and tetraenes preferentially onto their exo-face. The same face selectivity was observed for the cycloadditions of TCE to the (Z)- and (E)-chlorodienes 9 and 10 , thus realizing a case where the kinetic stereoselectivity of the additions is proven not to be governed by the stability of the adducts. The exo-face selectivity of the Diels-Alder additions of dienes grafted onto 7-oxabicyclo [2,2.1]heptanes contrasts with the endo-face selectivity reported for a large number of cycloadditions of dienes grafted onto bicyclo[2.2.1]heptane skeletons.     

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 ).     

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.     

Face Selectivity of the Diels-Alder Reaction of 5,6-Bis((D)methylidene)-2-bicyclo[2.2.2]octene

The face selectivity (endo-face vs. exo-face attack onto the exocyclic s-cis-butadiene moiety) of the [4+2]cycloadditions of 5,6-bis((D)methylidene)-2-bicyclo-[2.2.2]octene ( 11 ) to strong dienophiles has been determined in benzene at 25°. It is ca. 95/5, 75/5, 70/30, 60/40 and 50/50 for N-phenyltriazolinedione (NPTAD), tetracyanoethylene (TCE), dimethyl acetylenedicarboxylate (DMAD), maleic anhydride (MA) and singlet oxygen (¹O₂), respectively. The endo-face preference is probably due to a participation of the homoconjugated double bond at C(2), C(3) which makes the etheno bridge more polarizable than the ethano bridge in 11. The absence of face selectivity with ¹O₂ is consistent with an entropy-controlled mechanism involving the intermediacy of an exciplex.     

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).     

Manganese(III)-mediated facile synthesis of 3,4-dihydro-2(1H)-quinolinones: selectivity of the 6-endo and 5-exo cyclization

The 4,4-bis(ethoxycarbonyl)-3,4-dihydro-2(1H)-quinolinones 2 were easily synthesized by the oxidative 6-endo-trig cyclization of 2-[2-(N-arylamino)-2-oxoethyl]malonates 1 with manganese(III) acetate in good to excellent yields. The same reaction of N-(2,4-dimethoxyphenyl)-substituted malonate 1t exclusively produced the 5-exo-cyclized 4,4-bis(ethoxycarbonyl)-1-azaspiro[4,5]deca-6,9-diene-2,8-dione 5t instead of the corresponding dihydroquinolinone. The regioselectivity during the cyclization could be explained by the difference in the activation energy of the transition state of the 6-endo/5-exo cyclization.     

The Effects of Homoconjugated Cyclopropane and Oxirane Rings on the Diels-Alder Reactivity of 2,3-bis (methylidene)norbornane

Preparation of 6exo, 7exo-bis (methylidene)-tricyclo[3.2.1.0^2,4]octane ( 6 ) is described. The reactivity of 6 towards tetracyanoethylene is evaluated and compared with that of exo-2,3-epoxy-5,6-bis (methylidene)norbornane ( 5 ), 2,3-bis-(methylidene)norbornane ( 1 ) and other related dienes. The cyclopropane group in 6 exerts an unsignificant rate retardation effect on the Diels-Alder reactivity of this diene relative to that of 1 , whereas a relatively important rate retardation effect is caused by the exo-oxirane ring in 5 . The observed effects are probably due to electronic factors (through-space and through-bond interactions).     

Stereoselective Synthesis and Diels-Alder Reactions of (Z)- and (E)-1,2-bis(Phenylthio)-1,3-Butadiene

Bromination of 3-phenylthio-2-sulfolene (2) with N-bromosuccinimide gave 2-bromo-3-phenylthio-2-sulfolene (3) which was converted mainly to 2,3-bis(phenylthio)-2-sulfolene (4) by treatment with sodium phenylthiolate. Thermal desulfonylation of 4 at different temperatures in the presence of a base (DBU) yielded stereoselectively the (Z)- and (E)-1,2-bis(phenylthio)-1,3-butadiene (6). These two geometric isomers could be thermally interconverted. The Diels-Alder reactions of 6 were also investigated. Only the (Z)-diene 6a could undergo the Diels-Alder reaction; the (E)-diene 6b was in situ converted to the Z isomer before undergoing (he Diels-Alder reaction. The reaction of 6a with N-phenylmaleimide gave the cycloaddition product 7 with complete endo selectivity, but under daylight or during chromatography it readily underwent a thioallylic rearrangement to yield 8 with inversion of configuration. The cycloaddition of 6a with methyl acrylate proceeded regiospecifically, but generating a mixture of endo and exo isomers. The endo/exo ratio could be increased by using ZnCl₂ as the catalyst.     

Stereochemical studies. 81. Saturated heterocycles. 69 . Preparation of methylene-bridged 3,1-benzoxazines, 3,1-benzoxazin-2-ones and 3,1-benzoxazine-2-thiones

3-exo-Aminobicyclo[2.2.1]hept-5-ene-2-exo-carboxylic acid and ethyl 3-endo-aminobicyclo[2.2.1]heptane-2-endo-carboxylate ( 6 ) were reduced with lithium aluminum hydride to the corresponding bicyclic aminoalcohols 3 and 4 . These and the saturated endo-endo and exo-exo N-methylaminoalcohols 16 and 22 , respectively, were converted to methylene-bridged tetrahydro- ( 11 ) and hexahydro-3,1-benzoxazin-2-ones 12, 17, 23 and 3,1-benzoxazin-2-thiones 13, 14, 18, 24 . The exo-exo 3 and endo-endo 4 aminoalcohols were cyclized by means of ethyl arylimidates to tricyclic dihydro-1,3-oxazines 7a-d, 8a-d . The structures were confirmed by ir, ¹H and ¹³C nmr spectroscopy.     

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).     

Synthesis and Ritter Reaction of 3-exo-Hydroxymethyl-5,5,6-trimethylbicyclo[2.2.1]heptan-2-one

3-exo-Hydroxymethyl-5,5,6-trimethylbicyclo[2.2.1]heptan-2-one was prepared by treatment of isocamphanone with Paraform in the presence of alkali in DMF. The product reacts with acetonitrile in the presence of sulfuric acid (Ritter reaction) to form a mixture of 2-(acetylamino)-3-(acetylaminomethyl)-5,5,6-trimethylbicyclo[2.2.1]hept-2-ene and 2,2-bis(acetylamino)-3-(acetylaminomethyl)-5,5,6-trimethylbicyclo[2.2.1]heptane in a 1:1 ratio. Attempted hydroxymethylation of isocamphanone in DMSO gave bis(isocamphanon-3-endo-yl)methane.     

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.     

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.     

Carbon Participation in the Solvolysis of Tertiary Norbornyl Derivatives Norbornanes. Part 15. 6-substituted 2-methylnorbornyl 2-exo- and 2-endo-2,4-dinitrophenyl ethers

The solvolysis rates and products of the tertiary 2-methyl-2-exo- and -2-endo-norbornyl 2,4-dinitrophenyl ethers 1 and 2 , (X = 2,4-(NO₂)₂₂C₆H₃O) have been determined. The different sensitivities of the rates of these ethers to the inductive effect of substituents at C(6) indicate that graded bridging of C(2) by C(6) occurs in the ionization of the exo-ethers 1 , not, however, in the ionization of the endo-ethers 2. In both cases hydrolysis leads to 2-methyl-2-exo-norbornanols only. Consequently, substitution takes place with retention at C(2) in the exo-series 1 and with inversion at C(2) in the endo-series 2. It is concluded that stereoelectronic and polar effects, rather than steric bulk effects, determine the high exo/endo rate ratios of the parent norbornyl derivatives 1a and 2a .     

Synthesis of Polypropionate Fragments Containing Tertiary-Alcohol Moieties. Cross-aldolisations with lithium enolates of 7-oxabicyclo[2.2.1]heptan-2-one derivatives

The Diels-Alder adduct of 2,4-dimethylfuran to 1-cyanovinyl (1′R)-camphanate ((+)-(1R,2S,4R)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′R)-camphanate ((+)- 1 )) was converted into (+)-2,7-dideoxy-2,4-di-C-methyl-L -glycero- ((+)- 6 ) and -D -glycero-L -altro-heptono-1,4-lactone ((+)- 7 ), into (?)-(3R,4R,5R,6S)-3,4:5,7-bis(isopropylidenedioxy)-4,6-dimethylheptan-2-one ((?)- 22 ), and into (+)-(2R,3R,4R,5S,6S)-3,4:5,6-bis(isopropylidenedioxy)-2,4-dimethylheptanal ((+)- 34 ). Condensation of ((+)- 34 with the lithium enolate of (?)-(1R,4R,5S,6R)-6-exo-[(tert-butyl)dimethylsilyloxy]-1,5-endo-dimethyl-7-oxabicyclo[2.2.1] heptan-2-one ((?)- 38 ; derived from (+)- 1 ) gave a 3:2 mixture of aldols (+)- 39 and (+)- 40 (mismatched pairs of a α-methyl-substituted aldehyde and (E)-enolate) whereas the reaction of (±)- 34 with (±)- 38 gave a 10:1 mixture of aldols (±)- 41 and (±)- 39 . A single aldol, (?)- 44 , was obtained to condensing (+)- 34 with the lithium enolate of (+)-(1S,4S,5S,6S)-5-exo-(benzyloxy)-1,5-endo-dimethyl-7-oxabicyclo[2.2.1]heptan-2-one ((+)- 43 ; derived from (?)-(1S,2R,4S)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′S)-camphanate ((?)- 3 )). All these cross-aldolisations are highly exo-face selective for the bicyclic ketones. The best stereochemical matching is obtained when the lithium enolates and α-methyl-substituted aldehydes can realize a ‘chelated transition state’ that obeys the Cram and Felkin-Anh models (steric effects). Polypropionate fragments containing eleven contiguous stereogenic centres and tertiary-alcohol moieties are thus prepared with high stereoselectivity in a convergent fashion. The chiral auxiliaries ((1R)- and (1S)-camphanic acid) are recovered at the beginning of the syntheses.     

Synthesis of 3-Methyleneisoindolin-1-ones and Isoquinolinium Salts via Exo and Endo Selective Cyclization of 2-(1-Alkynyl)benzaldimines

Coinage metal-promoted 5-exo and 6-endo selective cyclization of 2-(1-alkynyl)benzaldimines has been studied. It was found that, under gold catalysis, 2-(1-alkynyl)benzaldimines exclusively underwent 5-exo-dig cyclization processes, followed by oxidation to form N-aryl 3-methyleneisoindolin-1-ones. In contrast, in the presence of base and under activation of AgOTf, switching of 5-exo to 6-endo cyclizations of 2-(1-alkynyl)benzaldimines was observed, exclusively giving N-aryl or N-alkyl substituted isoquinolinium salts. The two key reaction intermediates, exocyclic vinyl-Au and the endocyclic vinyl-Ag species have been isolated and characterized, and a study of their reactivities confirms the plausible mechanisms. Reactions of the resultant 3-methyleneisoindolin-1-ones with benzyne afforded structurally important isoindolinone-based benzocyclobutenes. Additionally, several interesting transformations of the resultant isoquinolinium salts have been investigated.     

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).     

Reduction of 5,6-Dimethylidene-exo-2,3-epoxynorbornane with Metal Hydrides. Efficient syntheses of 6-methyl-5-methylidene-anti-3- nortricyclanol and of 2,3-dimethylidene-anti-7-norbornanol

5,6-Dimethylidene-exo-2,3-epoxynorbornane ( 1 ) is reduced slowly by LiAlH₄ in boiling tetrahydrofuran (THF) and furnishes a mixture of 5,6-dimethylidene-exo-2-norbornanol ( 2 ), 2,3-dimethylidene-anti-7-norbornanol ( 3 ) and principally 6-methyl-5-methylidene-anti-3-nortricyclanol ( 4 ). The yield of 4 is the highest for low initial concentrations of LiAlH₄; it decreases in favour of alcohols 2 and 3 at high concentration of LiAlH₄. The reduction of 1 with AlH₃ in THF yields 3 as the major product, thus revealing an efficient synthesis of 7-substituted-2, 3-dimethyl-idenenorbornane derivatives. No alcohol 2 could be isolated by LiEt₃BH reduction of 1 . LiAlD₄ reduces 1 into the monodeuterated alcohols 2 -d, 3 -d and 4 -d. The deuterium label is found in the endo-position at C (3) in 2 -d, in the exo-position at C(5) in 3 -d and in the methyl group of the tricyclic alcohol 4 -d. Mechanistic limits for the formation of 2 , 3 and 4 are discussed briefly.