Olefins, deuterated

The fact that Schrock s proposed metallocyclobutanes decomposed to propylene derivatives rather than cyclopropanes was fortunate in that further information resulted regarding the stereochemistry of the olefin reaction with the carbene carbon, as now the /3-carbon from the metal-locycle precursor retained its identity. The reaction course was consistent with nucleophilic attack of the carbene carbon on the complexed olefin, despite potential steric hindrance from the bulky carbene. Decomposition via pathways f-h in Eq. (26) was clearly confirmed in studies utilizing deuterated olefins (67). 

Scheme 5 Site selectivity of the photo-oxygenation of deuterated olefins (cis effect).

While these reactions are of limited use in the synthesis of complex molecules, they are very interesting from a mechanistic point of view. It has been firmly established that benzylic or allylic radicals and metal centered radicals are formed as intermediates through hydrogen atom transfer from the M-H bond to the C-C double bond. Interestingly, the addition of the hydrogen atom is reversible as demonstrated by isotope scrambling with deuterated olefins. If the radicals possess multiple sites for hydrogen atom abstraction, olefin isomerization can ultimately occur. HAT to unactivated olefins was not observed. 

The a-(diphenylmethylsilyl) esters have been shown to be vinyl dication equivalents 3, and as such are precursors to terminal olefins and deuterated olefins, 1,1-dlsubstituted olefins and tri- and tetrasubstituted olefins. ... 

Proof for this mechanism is found from the high cisitrans ratios of the isomer-ized olefin formed at an early stage in the reaction [16], and little or no deuterium substitution in the 2-position (J3) when deuterated olefins are being used an example is shown in eq. (6). 

Later, it was possible to improve substantially the separation of deuterated olefins. Atkinson et al. [67], for example, separated all ethylene isomers differing by one unit of mass. It was shown that the accuracy of the gas chromatographic analysis of deuterium-labelled ethylene isotopes is the same as that in the mass spectral method. Silver nitrate solution in ethylene glycol (5M), saturated at room temperature, was used as the stationary phase [67]. This solution was added to Chromosorb P (45—60 mesh) in the ratio of 1 4 and this mixture was mechanically stirred for 4 h. The sorbent obtained was packed into nylon tube sections of length 15 m and diameter 3 mm. A flame-ionization detector was used. 

The separation of deuterated butenes gave the following relative retention times (relative to the non-deuterated) cis-1-butene-1-dj, 1.036 frans-l-butene-l-dj, 1.027. It can be seen that the use of a solution of silver nitrate in ethylene glycol enables good separations of deuterated olefins to be achieved. Unfortunately, the separation time is long (about 5 h), but can probably be reduced by the use of more efficient capillary columns and optimization of the separation conditions in particular, as the separation temperature is decreased the selectivity increases sharply. 

This method for the separation of deuterated olefin isomers has been used successfully by Ache and Wolf [66]. Fig. 6.2C shows the separation of ethylene (1), ethylene-d, (2) and ethylene-dj (3) by circular chromatography. The separation obtained at the ninth cycle took about 100 min. Successful separation of the deuterated olefins on columns containing a complexing stationary phase, i.e., silver nitrate solution in ethylene glycol, gave the possibility of separating isotopic olefin position isomers labelled also with tritium. Lee and Rowland [65] demonstrated the possibility of this separation. Fig. 6.2D shows the separation of ethylene (1), ethylene-t, (2) and propylenes CHj H—CH=CH2... 

An interesting method for the preparation of deuterated olefins starts with addition of a dialkylaluminum deuteride (or hydride) to an acetylenic bond. Hydrolysis of the unsaturated organoaluminum compound resulting from the... 

By the use of deuterated dialkylaluminum hydride for the addition and/or heavy water for hydrolysis, specifically deuterated olefins may be prepared. Likewise, hydroboration of certain olefins has now been shown to occur in a cis-fashion (16). 

Supporting evidence against irreversible intermediate formation is found in some unpublished studies by H. G. Vilhuber (i5), E. Werstiuk (16), and V. Chuang (3) on the primary deuterium isotope effect. Primary isotope effects of 1.2 to 2.1 were determined for deuterated olefins 34-36,... 

The a-(diphenylmethylsilyl) esters have been shown to be vinyl dication equivalents 3, and as such are precursors to terminal olefins and deuterated olefins, 1,1-disubstituted olefins and tri- and tetrasubstituted olefins. They are precursors to B-ketosilanes and ketones, wherein the overall transformation results in an ester to ketone conversion. They can also be deprotonated and the enolate anion condensed with aldehydes and ketones to give a,6-unsaturated esters, in particular a-alkylated-a,B-unsaturated esters. Their y-lactone counterparts, o-(diphenylmethy1snyl )-y-butyrolactone 4a and a-(diphenylmethylsilyl)-y-valerolactone 4b, are precursors to 4-oxo acids,1,4-diketones and a-ylidene-y-lactones. ... 

The catalytic system Co2(CO)gH-H2 forms the complex CoH(CO)4, which has strongly acidic character in polar solvents. Therefore, the complex CoH(CO)4 is more likely to be added to 1-alkenes according to the Markovnikov rule than RhH(CO)(PPh3)3. Based on the studies of hydroformylation of deuterated olefins, it was proposed that the addition-elimination process proceeds according to the concerted mechanism (13.60)... 

In a concerted process, an olefin can add cis or trans to MA. These are represented as syn-syn and anti-anti concerted processes and are symmetry allowed.We have seen that the predominant product obtained is a trans-olefin however, thermodynamic stabilities of the products cannot be ruled out as a contributing factor. To eliminate this stability bias, Friedrich et al have investigated the reaction of 2,3,3-trimethyl-l-butene 68 and its deuter-ated analogue. From the NMR of the product, it was concluded that starting with deuterated olefin, H2 and H3 (i.e., those originating from MA) were cis. Since the limit of detectability of the other isomer is 30%, it may be concluded that the ene reaction is at least 70% c/5-stereospecific. 

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