Spiroacetals from Acetone and Oxiranes - A Simple Route to Optically Active 1,6-Dioxaspiro [4,4]nonane-pheromones

Enders, Dieter; Dahmen, W.; Dederichs, E.; Weuster, Peter

doi:10.1080/00397918308063739

Cited by 14 publications

(1 citation statement)

References 13 publications

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“…10 The lithiated N,N-dimethylhydrazone of acetone generated also clean S N 2 products with optically active oxiranes as reported by Enders et al in ref. [21]. 11 See ref.…”

Section: Oxiranes As Electrophiles Combined With Iodomethanementioning

confidence: 99%

Regioselective Dialkylations of N‐(tert‐Butyl)iminocyclopentane via Deprotonating One‐Pot Procedures

Knorr

Neuner

2018

Helvetica Chimica Acta

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The title compound (1) was chosen as a model for the α/α′‐regioselectivity of deprotonation and subsequent alkylation adjacent to the C=N bond. With the bulky base lithium N,N‐diisopropylamide (LDA) as a catalyst, the one‐pot deprotonation steps can be performed through titration with methyllithium, using gas‐volumetric observation of the liberated methane. In the first step with ensuing methylation by iodomethane, the primary product is born at −40 °C in its metastable (Z) configuration (kinetic control) and may be either isolated or converted in situ at 30 °C into its thermodynamically favored (E)‐isomer via cis to trans stereoinversion at the N‐atom. Being slow enough on the laboratory time scale, this stereoinversion process can serve to control the regioselectivity of the second deprotonation/alkylation sequence as follows. The α,α′‐products are formed from the intermediate (Z)‐imine, whereas α,α‐products result from the intermediate (E)‐imine; in either case, syn deprotonation (cis to tBu at nitrogen) by LDA is apparently disfavored by the tBu group, so that anti deprotonation becomes obligatory. If a third one‐pot deprotonation step is too slow with LDA, it may be performed with the stronger base butyllithium/HMPA which, however, reacts regio‐unselectively. Regioselective one‐pot, LDA‐catalyzed deprotonation with alkylation by oxiranes (alone, or alternatingly with iodomethane) opens a short access to spiro‐[2.4]heptan‐4‐ones.

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“…10 The lithiated N,N-dimethylhydrazone of acetone generated also clean S N 2 products with optically active oxiranes as reported by Enders et al in ref. [21]. 11 See ref.…”

Section: Oxiranes As Electrophiles Combined With Iodomethanementioning

confidence: 99%

Regioselective Dialkylations of N‐(tert‐Butyl)iminocyclopentane via Deprotonating One‐Pot Procedures

Knorr

Neuner

2018

Helvetica Chimica Acta

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Determination of Interconversion Barriers by Dynamic Gas Chromatography: Epimerization of Chalcogran

Trapp

Schurig

2001

Chem. Eur. J.

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The four stereoisomers of chalcogran 1 ((2RS,SRS)-2-ethyl-1,6-di-oxaspiro[4.4]nonane), the principal component of the aggregation pheromone of the bark beetle pityogenes chalcographus, are prone to interconversion at the spiro center (C5). During diastereo- and enantioselective dynamic gas chromatography (DGC), epimerization of 1 gives rise to two independent interconversion peak profiles, each featuring a plateau between the peaks of the interconverting epimers. To determine the rate constants of epimerization by dynamic gas chromatography (DGC), equations to simulate the complex elution profiles were derived, using the theoretical plate model and the stochastic model of the chromatographic process. The Eyring activation parameters of the experimental interconversion profiles, between 70 and 120 C in the presence of the chiral stationary phase (CSP) Chirasil-beta-Dex, were then determined by computer-aided simulation with the aid of the new program Chrom-Win: (2R,5R)-1: deltaG(++) (298.15 K) = 108.0 +/-0.5 kJ mol(-1), deltaH(++) = 47.1+/-0.2 kJ mol(-1), deltaS(++) = -204+/-6 JK(-1) mol(-1): (2R,5S)-1: deltaG(++) (298.15 K) = 108.5+/-0.5 kJ mol(-1), deltaH(++) = 45.8+/-0.2 kJ mol(-1), deltaS(++) = -210 +/-6 J K mol(-1); (2S,5S)-1: deltaG(++) (298.15 K)= 108.1+/-0.5 kJ mol(-1), deltaH(++) = 49.3+/-0.3 kJ mol(-1), deltaS(++) = -197+/-8 J K(-1) mol(-1); (2S,5R)-1: deltaG(++) (298.15 K)=108.6+/-0.5 kJ mol(-1), deltaH(++) = 48.0+/-0.3 kJ mol(-1), deltaS(++) = -203+/-8 J K(-1) mol(-1). The thermodynamic Gibbs free energy of the E/Z equilibrium of the epimers was determined by the stopped-flow multidimensional gas chromatographic technique: deltaG(E/Z) (298.15 K)= -0.5 kJ mol(-1), deltaH(E/Z) = 1.4 kJ mol(-1) and deltaS(E/Z) = 6.3 J K(-1) mol(-1). An interconversion pathway proceeding through ring-opening and formation of a zwitterion and an enol ether/alcohol intermediate of 1 is proposed.

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The Total Synthesis of Spiroketal‐Containing Natural Products

Vaillancourt

Pratt

Perron

et al. 1991

Total Synthesis of Natural Products

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Spiroacetals from Acetone and Oxiranes - A Simple Route to Optically Active 1,6-Dioxaspiro [4,4]nonane-pheromones

Cited by 14 publications

References 13 publications

Regioselective Dialkylations of N‐(tert‐Butyl)iminocyclopentane via Deprotonating One‐Pot Procedures

Regioselective Dialkylations of N‐(tert‐Butyl)iminocyclopentane via Deprotonating One‐Pot Procedures

Determination of Interconversion Barriers by Dynamic Gas Chromatography: Epimerization of Chalcogran

The Total Synthesis of Spiroketal‐Containing Natural Products

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