Cycloheptene oxide

Using substituted a-methylene-(3-acetoxy ketones 2-494 with R = Me, Et, iPr, Ph and LiOtBu as base, the yields of the cycloheptene oxide 2-498 could be greatly enhanced to up to 77 %, as in the case of2-498b. In addition, cyclooctene oxides can be prepared (though in lower yield and stereoselectivity) starting from a six-membered oxosulfonium ylide. 

The problem of diastereoselectivity in additions to cyclic radicals arising from the opening of bi- or tricyclic epoxides, e. g. cycloheptene oxide or norbornene oxide, has been addressed only recently [32], In the former case, reasonable selectivities can be obtained with titanocene dichloride (trans cis = 76 24), but excellent selectivities are observed with bis(tert-butyl)titanocene dichloride (transxis = 94 6), as shown in Scheme 12.17. 

Inaba and coworkers reported that a Ti-BINOL complex is an effective catalyst for the desymmetrization of epoxide 44 using primary amines as nucleophiles. Of significant note is the efficiency of this reaction, with only 1 mol% catalyst necessary to attain high yields and selectivities [Eq. (10.11)]. Unfortunately, this epoxide is uniquely effective in this reaction. Cycloheptene oxide, dihydrofuran oxide, and an acyclic version of 44 each provided negligible yields under these reaction conditions ... 

Cycloheptene oxide has long been known to undergo amd-catalysed hydration to traw-l, 2-dicloheptancdirf.1M> 840 More recent work by f opo and oo-workers, 4 however, has unoovered in addition the presence of cia-1. d-oyotohcptanediol (Eq. 036). The latter eau be... 

While this methodology could be extended to more-substituted cyclooctene oxides (Scheme 56, Equation 12), examination of cycloheptene oxide (Scheme 56, Equation 13) revealed the need for considerably longer reaction times, leading to reduced yields due to competing carbenoid-insertion pathways (cycloheptanone formation and reductive alkylation) <2002AGE2376, 2003OBC4293>. 

Cycloheptene oxide has long been known to undergo aoid-eatalysed hydration to fyaw-1,2-dicIoheptanedkd.t - > < More recent work by t ipo and oo-workera, however, haa uncovered in addition the pioseiMe of CM-l,4-oyn ohoptaDediol (Ei], 036). The latter can ba... 

A dramatic reverse in selectivity was observed for 2-substituted cyclohexene oxide by simply changing the t-butyl group to a TMS or trimethylgermyl group,as depicted in equation (8). Regiocontrol by the TMS group is further demonstrated in the corresponding cyclopentene and cycloheptene oxides. ... 

The conformation of cycloheptene oxide has been examined via the C nmr spectra of deuterated compounds on the basis of the temperature-dependence of the chemical shifts of the individual signals. In phenyl-substituted oxiranes, the C shifts have revealed the inductive and hyperconjugative effects of the oxirane ring, and thus the ring behaves as an electron-acceptor. " ... 

The method fails, however, in the attempted conversion of cycloheptene oxide (8) into tram-cycloheptene In this case, the reaction affords (trans-2-hydroxycyclo-heptyl)methyldiphenylphosphonium fluoroborate (9). 

Deprotonation of meso-cycloheptene oxide diastereoisomers 100 and 102, possessing a pseudoasymmetric C-5 carbon, led to the enantiomeric ketones... 

LiHMDS, the qrcloheptene oxide derivative 42 was obtained in lower yield (23%), whereas with substituted 41 and liOt-Bu as base, yields of 42 could be greatly enhanced up to 77% (R =i-Pr, R = Ph) [23b]. The cycloheptene oxides 42 are considered to be formed through Sj 2 substitution of yUde 40 on 41 and subsequent intramolecular Corey-Chaykovsky reaction of the resulting ylide 44 through intermediate 45 (Scheme 4.9). 

Seven-membered Rings.—The conformational analysis of cycloheptene oxide has been studied by and n.m.r. spectroscopy. The singlet due to the C-2 proton of [l,3,3- H3]cycloheptane oxide (3) separates into two peaks at low temperatures, the free energy of activation for interconversion of the two conformers being 7.9 kcal mol . The n.m.r. spectrum of undeuteriated cycloheptene oxide showed four... 

The deprotonation of epoxides was reported twice. A 4-substituted cycloheptene oxide (95) was deprotonated with an organolithium base in the presence of a chiral... 

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