6688-07-9Relevant academic research and scientific papers
On the stereochemical course of the addition of allylsilanes to aldehydes
Denmark, Scott E.,Weber, Eric J.,Almstead, Neil G.,Wolf, Larry M.
experimental part, p. 7701 - 7718 (2012/09/11)
Model compounds 3 and 5 have been studied to determine the orientation of the reacting double bonds in the transition state of the allylmetal-aldehyde addition. These models were designed to remove any intrinsic steric bias for the formation of the bicyclic products that would obfuscate a stereoelectronic contribution to the transition states. Model system 3 revealed a modest preference for the synclinal transition state, albeit in very low yields. Model system 5 underwent selective and largely Lewis acid independent cyclization primarily via a synclinal transition state. The high proximal selectivity observed in these cyclizations likely reflects the selectivity of an unhindered allylmetal-aldehyde addition for the synclinal transition state and results from a stereoelectronic preference, not an intrinsic steric bias, for the synclinal arrangement of double bonds.
A facile microwave-assisted Diels-Alder reaction of vinylboronates
Sarotti, Ariel M.,Pisano, Pablo L.,Pellegrinet, Silvina C.
supporting information; experimental part, p. 5069 - 5073 (2010/12/25)
The Diels-Alder reaction of vinylboronates can be easily performed using microwave irradiation giving excellent yields of the cycloadducts. Pinacol vinylboronate was the reagent of choice due to its stability towards hydrolysis, operational simplicity and yields of Diels-Alder products. To the best of our knowledge, this is the first example of microwave-assisted Diels-Alder reaction of boron-substituted dienophiles. Subsequent in situ oxidation of the cycloadducts with alkaline hydrogen peroxide afforded the alcohols efficiently.
Syntheses with organoboranes. IX. Vinyl- and 1-alkenyldichloroboranes as ethylene and 1-alkene equivalents for the Diels-Alder reaction
Zaidlewicz, Marek,Binkul, Jacek R.,Sokol, Wojciech
, p. 354 - 362 (2007/10/03)
Vinyl- and 1-alkenyldichloroboranes were used as dienophiles for the Diels-Alder reaction with representative aliphatic and cyclic 1,3-dienes. The organoborane adducts were transformed into the corresponding olefins either by protonolysis or by oxidation-mesylation-reduction. Direct protonolysis of the adducts gave in most cases mixtures of olefins whereas the reduction of mesylates with lithium triethylborohydride produced pure olefins in good yields.
4S,5S-[Bis(carbethoxy)]-2-ethenyl-1,3,2-dioxaborolane: A novel enantioselective dienophile
Bonk, Jason D.,Avery, Mitchell A.
, p. 1149 - 1152 (2007/10/03)
The novel chiral vinyl boronate (+)-1 was utilized as a dienophile in a series of [4+2] cycloadditions. The intermediate cyclized products obtained were oxidized directly (H2O2, NaOH). The resulting alcohols displayed enantiomeric excesses of 7-33%. A slight preference for the endo configuration was observed, in agreement with previous results.
Ouverture acidocatalysee d'epoxydes bicyclooctaniques: Intervention d'un mecanisme A2 avec retention de configuration
Plenat, Francoise,Renard, Gilbert,Christol, Henri
, p. 125 - 132 (2007/10/02)
During the stereochemical study of the products obtained by acid-catalysed ring opening of 2,3-endo epoxynorbornane, a concerted "front" attack mechanism has been brought to light.This can be explained by the known preference for intramolecular rather than intermolecular mechanisms.This acid-catalyzed ring opening has been extended to 2,3-epoxybicyclooctane, the bonds of which are in the same spatial position towards the epoxy carbon atoms and which can undergo anti and "front" attack of the epoxide ring.Products arising from both kinds of intramolecular attack can be isolated.In addition, the ring opening reaction of 2,3-endo and exo epoxy-5,6-trans-dicarbomethoxybicyclooctanes indicates that they proceed by a concerted mechanism, so that the "front" attack mechanism must be specially favourable to these bicyclic structures.Since the reactions considered are like bimolecular nucleophilic substitutions, for which the anti attack mechanism is known to be energetically favoured over the "front" attack, the following suggestions can be made to explain our results: there is steric hindrance to anti approach of the external nucleophile, torsional strain lowering and favourable orbital alignment for the "front" attack.
Electronic Structure of Symmetric Homocojugated Dienes. Circular Dichroism of (1S)-2-Deuterio- and 2-Methylnorbornadiene and (1S)-2-Deuterio- and 2-Methylbicyclooctadiene
Lightner, David A.,Gawronski, Jacek K.,Bouman, Thomas D.
, p. 5749 - 5754 (2007/10/02)
(1S)-Bicyclohepta-2,5-diene (1), (1S)-2-methylbicyclohepta-2,5-diene (3), (1S)-bicycloocta-2,5-diene (4), and (1S)-2-methylbicyclooctadiene (6) were prepared by reaction of the corresponding chiral β,γ-unsaturated ketone tosylhydrazone with CH3Li followed by either D2O or CH3I quenching.The circular dichroism Cotton effects of 1 (Δε237 = -0.032, Δε216 = +0.14, Δε205 = -0.37) and 4 (Δε222 = -0.027) are the first examples obtained from deuterated olefins or dienes whose chirality is due only to isotopic substitution.Both the deuterated and the methylated dienes exhibited multiple Cotton effects (3, Δε249 = +2.38, Δε222 = -0.25, Δε219 = -0.54, Δε214 = +0.62, Δε204 = -0.94; 6, Δε231 = +0.90, Δε211 = +0.48, Δε200 = -0.24), demonstrating the existence of interchromophoric interaction and electronic transitions that are only difficulty seen in their ultraviolet spectra.We present ab initio localized orbital RPA calculations on 1 that allow a consistent assignment of norbornadiene transitions.
