“…These results suggest that the diazoselenoketone 13 doesnot undergo cyclization to the corresponding selenadiazoline 14 to give 7, but further selenation to lead to 12 which reacts with elemental selenium to yield 11. Although 13 may be in equilibrium with 14 [2,18,19], the equilibrium would lie predominantly towards 13.…”
“…These results suggest that the diazoselenoketone 13 doesnot undergo cyclization to the corresponding selenadiazoline 14 to give 7, but further selenation to lead to 12 which reacts with elemental selenium to yield 11. Although 13 may be in equilibrium with 14 [2,18,19], the equilibrium would lie predominantly towards 13.…”
“…The chemistry of sterically congested alkenes has been a most challenging subject in both synthetic chemistry − and theoretical chemistry 7 for the last several decades. An ultimate goal of this chemistry is the preparation of tetra- tert -butylethylene ( 1 ).…”
Section: Introductionmentioning
confidence: 99%
“…An ultimate goal of this chemistry is the preparation of tetra- tert -butylethylene ( 1 ). Although the 2-fold extrusion process 1 (route A, eq 1) and the McMurry coupling 2 using low-valent Ti (route B, eq 1) have been satisfactorily applied to the synthesis of sterically congested alkenes, the compound 1 has never been synthesized despite extensive effort. − …”
Section: Introductionmentioning
confidence: 99%
“…The preparation of tied-back cyclic alkenes as intermediates has been considered to be a potential strategy for the synthesis of 1 ; the tying would facilitate the synthesis by moderating the steric hindrance between the adjacent tert -butyl groups, and untying might give 1 . − This approach led to the synthesis of tetrakis(2-formyl-2-propyl)ethylene ( 2 ) from bi-3,3,5,5-tetramethylcyclopentene-4-ylidene ( 3 ) 3h,4,5 and tetrakis(1-methylcyclopropyl)ethylene ( 4 ) 6 as the most successful examples, but the synthesis of sulfur-bridged tied-back alkenes 5 , 3h,i,4c 6 ,3a and 7 3g has not been accomplished yet. …”
Two sterically congested cycloalkenes (9 and 10), congeners of tetra-tert-butylethylene, were synthesized and characterized. Oxidation of the bicyclic 1,3-dithietane 8 with dimethyldioxirane (DMD) gave the endo,endo-disulfoxide 13, thermal isomerization of which to the endo,exo-disulfoxide 15 followed by oxidation with DMD gave the trioxide 18. Heating 18 in refluxing 1,3-dimethyl-2-imidazolidinone furnished 1,2-di-tert-butyl-3,3,5,5-tetramethylcyclopentene (9) in 69% yield by a 2-fold extrusion process. The reaction of the 1,6-diketone dihydrazone 23 with Se(2)Cl(2) gave the selenadiazoline 34 and the 1,3-diselenetane 35. Heating 34 at 115-130 degrees C gave 1,2-di-tert-butyl-3,3,6,6-tetramethylcyclohexene (10), a "didehydro" derivative of tetra-tert-butylethylene, in 43% yield. The C=C bond in 10 is strained in degree comparable to those of most strained alkenes reported so far.
“…The reaction of a diazocyclopentane 15 17 (2.4 molar equiv) with S 2 O (method I) yielded the spirodithiirane 1‐oxide 16 (0.21 molar equiv) along with azine 17 17 (0.17 molar equiv) [Eq. (3)].…”
Ein Dischwefelmonoxid‐Äquivalent („S2O“) ist das Ergebnis der Oxidation von elementarem Schwefel (S8) mit Dimethyldioxiran (oder wahlweise mit CF3CO3H). Die Ausbeute an „S2O“ beträgt bei Verwendung äquimolarer Mengen an S8 und dem Oxidationsmittel 30–40 %; mit Diazoalkanen reagiert es zu Dithiiran‐1‐oxiden [Gl. (1)].
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