π-Electron Participation in the Acetolysis of β-(<i>syn</i>-7-Norbornenyl)ethyl <i>p</i>-Bromobenzenesulfonate

Bly, Robert S.; Bly, Ruta K.; Bedenbaugh, Angela O.; Vail, Oakley R.

doi:10.1021/ja00980a026

Cited by 17 publications

(13 citation statements)

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“…Relative g.1.p.c. retention times on Carbowax were also consistent with thqse previously established, "syn-01s" eluting before "anti-01s" (2,3,7 stereochemistry is the 0-H stretching pattern in the i.r. spectrum.…”

Section: Introductionsupporting

confidence: 89%

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Reactions of Norbornen-7-one with Organolithium Reagents

Clark¹,

Warkentin²

1971

Can. J. Chem.

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Alkyllithium reagents (RLi: R = methyl, 11-butyl, t-butyl) add to norbornen-7-one either without stereochemical preference (R = n-butyl) or with syn attack favored. This addition selectivity is qualitatively the same as that shown by corresponding alkylmagnesium reagents but competition from reduction is much less important in the case of alkyllithium reagents.Phenyllithium and vinyllithium add preferentially from the anti face, although the corresponding Grignard reagents add selectively from the syn face. Possible causes of the stereoselectivities are considered. Solvent effects on the stereochemistry of addition are small. L'addition des alkyl-lithium (RLi ou R = Me, 11-Bu, t-Bu) k la norbornkn-7 one se fait soit sans prCfCrence stCrCochimique (R = 11-Bu) soit avec une attaque syn favorisCe. La ~Clectivitt de cette addition est qualitativement la mCme que celle observCe lors de I'action des organomagnesiens correspondants mais la compCtition des rCactions de rCduction est beaucoup moins importante avec les organo-lithiens.Quoique les organomagntsiens correspondants s'additionnent ~Clectivement par la face syn, le phCnyllithium et le vinyl-lithium s'additionnent prCferentiellement par la face anti. On considere les causes possibles de ces stCrCosClectivitCs. Les effets de solvants sur la stCrCochimie de ces additions sont faibles.

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Section: Introductionsupporting

confidence: 89%

“…Relative retention times in g.1.p.c. and intramolecular hydrogen bonding in syn-01s (3,4,7) have served as criteria of configuration. Warkentin (2) used the g.1.p.c.…”

Section: Introductionmentioning

confidence: 99%

Reactions of Norbornen-7-one with Organolithium Reagents

Clark¹,

Warkentin²

1971

Can. J. Chem.

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“…These are probably influenced by the carbonyl group: the site of the carbenium ion has a tendency to move away from the carbonyl group, and not to be in the axis of the dipole C=O. Nevertheless this influence cannot be very important; this can be seen in the comparison of ow result with those obtained by Bly et al [17]: the B-(syn-7-norbornenyl)ethyl brosylate cyclization forms, in the absence of a carbonyl group, 42% of 2-exo-brendyl acetate, 36% of 4-exo-brexyl acetate and 22% of deltacyclane; this product distribution is comparable with our result: 28% of brendyl, 47% of brexyl and 25% of deltacyclanyl derivatives, 8,9, and 7.…”

mentioning

confidence: 55%

“…-The results of products analysis agree with those of kinetics; l a presents strong anchimeric acceleration (3 835-fold) and 100% cyclization, whereas in 3a participation is weak (acceleration -2-fold and 27% cyclization). A similar difference of participation between the position 7-syn and 5-endo of 2-norbornene was found in the acetolysis of brosylates R-CH2-CH2-OBs: Bly et al [17] found 140,000-fold acceleration and 100% cyclization when the brosyloxyethyl group was in the position 7-syn of 2-norbornene, whereas Allred & Maricich [25] found only 15-fold acceleration and ca. 95% cyclization for the 5-endo position.…”

mentioning

confidence: 61%

“…Thus the 835-fold acceleration of the global reaction rate represents only the minimum value of the anchimeric effect; the true acceleration of the substitution step cannot be measured. In comparison, Bly et al [17] have found in the rate of the acetolysis of 7-synbrosyloxyethyl-2-norbornene a 140,000-fold acceleration over that of the saturated analogue.…”

Section: Discussionmentioning

confidence: 90%

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π‐Participation in Diazoketone Hydrolysis II; Exo‐endo Cyclization Ratio in the Hydrolyses of 7‐syn‐ and 5‐endo‐Diazoacetyl‐2‐norbornene

Malherbe

Dahn

1977

Helvetica Chimica Acta

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SummaryThe rate of the acid-catalysed hydrolysis of 7-syn-diazoacetyl-2-norbornene (la) is enhanced relative to that of the saturated analogue 5a by a factor of 835. In contrast to the behaviour of other primary diazoketones, the substitution step is no longer rate-determining (mechanism A -2), but so much accelerated that the preceding proton transfer becomes the slow step (mechanism A-SE2, demonstrated by a solvent isotope effect kH/kD = 1.76). Product analysis shows 100% cyclization; the product formation is explained in terms of brexyl and brendyl type carbenium ions (or ion pairs). -5-endo-Diazoacetyl-2-norbornene (3a) shows very slight acceleration, and forms only 27% cyclization products (identical to those formed from la). Thus, in spite of the absence of steric hindrance by hydrogen atoms, the exo-endo rate ratio for anchimeric assistance is 3 lo3.Acid-catalysed hydrolysis of primary diazoketones follows the A -2 mechanism, rapid preequilibrium protonation forming a diazonium ion, followed by ratedetermining substitution [2] by a nucleophile. As the diazonium group is very sensitive, a weak nucleophile, for instance H 2 0 [3], is sufficient.H' , rapid R-CO-CHN, FR-CO-CHZNZ H20 ,R-CO-CH,OH+ N2+ H+ rate-det.A double bond in 5,6-position relative to the diazomethyl group can compete with a weak external nucleophile and form cyclic products [l] [4] [5]. The neighbouring group participation can furthermore result in a rate enhancement; we found this particularly with methylated cyclic olefins: 4-diazoacetyl-1,2-dimethylcyclopent-1-ene is hydrolysed about ten times more rapidly than diazoacetylcyclopentane [5]. We now present the results of a study of the hydrolyses of compounds in which the diazoacetyl group is kept in a rigid framework; 7-syndiazoacetyl-2-norbornene (la) and its anti isomer (2a), 5-endo-diazoacetyl-2-norbornene (3a) and its exo isomer (4a) have been compared with the saturated analogues 7-diazoacetyl-and 2-endo-diazoacetyl-norbornanes (5 a, 6 a).

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Synthetic Applications of Phosphoryl‐Stabilized Anions

1977

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The successful synthesis of a wide variety of unsaturated compounds by treatment of phosphoranes with carbonyl compounds (the Wittig reaction) has stimulated the search for other synthetic methods that employ organophosphorus reagents. One of the most fruitful results has been the discovery that phosphoryl‐stabilized carbanions have wide applicability in the preparation of unsaturated compounds and offer significant advantages over conventional procedures. This review discusses the chemistry of carbanions stabilized by delocalization of their negative charge by means of a P(O) group. Carbanions obtained by treating phosphine oxides, phosphinates, and phosphonates, with a base have been explored in depth. In particular, the phosphonates have found great popularity because of their availability and ease of application. The use of Wittig‐type reagents in synthesis has been reviewed and is not mentioned except by way of comparison. Carbanions prepared from phosphinates have no known advantage over those prepared from phosphonates or phosphine oxides. Those carbanions obtained from phosphine oxides will be considered here only in the way of comparison. Anions that have their negative charge located on an atom adjacent to a P(O) group gain stability owing to delocalization of the charge through the phosphoryl group. Although the exact nature of the delocalization is not well defined, the ability of phosphorus to become pentacovalent by use of its d orbitals is undoubtedly a contributing factor. It should be noted that the P(O) group is generally not so effective as the carbonyl group in stabilizing a negative charge. If other stabilizing groups are not present, formation of P(O)‐stabilized carbanions generally requires more basic conditions than does the removal of a proton from a carbon atom alpha to a carbonyl group. Horner and co‐workers were the first to investigate the synthetic utility of P(O)‐stabilized carbanions. The utility of phosphonate carbanions as synthetic intermediates was expanded by the discovery that, as olefin‐forming reagents, phosphonates have certain advantages over both phosphoranes and phosphine oxides. As a result, the method has found favor because of the availability of reagents, ease of workup, and convenient reaction conditions. In particular, the reactivity of phosphonate carbanions has been taken advantage of in numerous ways. As indicated by a number of reviews, these carbanions have become one of the most frequently employed organophosphorus reagents. The utility of phosphoryl‐stabilized anions is apparent from the variety of materials that can be prepared by suitable structural modifications. Besides simple monoolefins and polyenes, a partial list would include allenes, unsaturated amides, aldehydes, esters, sulfides, sulfones, and nitrogen compounds such as imines, isocyanates, and ketenimines. In addition to their convenience for introducing unsaturation, these stabilized anions offer routes to cyclopropanes and heterocyclic systems. In this chapter, reactions that are of unusual interest are discussed separately; more routine reactions are included only in the tabular survey. Olefin formation by means of phosphonate carbanions has been referred to as the Horner‐Emmons or Wadsworth‐Emmons modification of the Wittig reaction, whereas the use of phosphine oxide or phosphinate carbanions is generally referred to as the Horner modification. In order to prevent confusion and to avoid misdirecting credit, proper names are omitted and the synthesis of an olefin by phosphonate carbanions is termed phosphonate‐olefin formation. Likewise, the term phosphine oxide‐olefin formation is employed where appropriate.

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π-Electron Participation in the Acetolysis of β-(syn-7-Norbornenyl)ethyl p-Bromobenzenesulfonate

Cited by 17 publications

References 0 publications

Reactions of Norbornen-7-one with Organolithium Reagents

Reactions of Norbornen-7-one with Organolithium Reagents

π‐Participation in Diazoketone Hydrolysis II; Exo‐endo Cyclization Ratio in the Hydrolyses of 7‐syn‐ and 5‐endo‐Diazoacetyl‐2‐norbornene

Synthetic Applications of Phosphoryl‐Stabilized Anions

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