Deuterium benzaldehyde

Fredenhagen und Bonhoeffer (SI) fiihrten die CANNIZZARO-Reak-tion mit Benzaldehyd in D20 durch und fanden dabei kein Deuterium in der CH2-Gruppe des entstandenen Benzylalkohols. Dies kann durch Wanderung des Wasserstoffs als Hydridion erklart werden. 

Es wurde kein Deuterium im Benzaldehyd gefunden das Alanin enthielt jedoch zwei Atomaquivalente davon, wahrscheinlich in der Methylengruppe. Das laBt sich durch folgende Tautomerie erklaren CH3 CHa... 

Table 40 The primary and secondary deuterium-tritium and hydrogen-tritium KIEs for the oxidation of benzyl alcohol to benzaldehyde with NAD+ and yeast alcohol dehydrogenase at 25°C.a...

If methyl iodide was used instead of deuterium oxide, compound 236 was obtained, along with the product of N-methylation. Using benzaldehyde or benzophenone as the electrophile gave the cyclized products 237 and 238, respectively <1989AP291>. 

Asymmetric transfer hydrogenation of benzaldehyde-l-d with (R,R)-28 and (CH3)3COK in 2-propanol gave (R)-benzyl-l-d alcohol quantitatively in 98% ee (Scheme 41) [114], Introduction of electron-donating and electron-accepting groups at the 4 position had little effect on the enantioselectivity. Catalytic deuteration of benzaldehydes was achieved by use of the same complex (R,R)-28 and a 1 1 mixture of formic acid-2-d and triethylamine to give the S deuter-io alcohols in up to 99% ee (Scheme 42) [114], The dt content in the product alcohol was >99%. Only a stoichiometric amount of deuterium source is required to complete the reaction. 

Elimination reactions of ( )- and (Z)-benzaldehyde Opivaloyloximes (19a) and (19b) with DBU in MeCN have been found to occur by a nitrile-forming E2 mechanism which is ca 2000-fold faster for the latter isomer in each case.15 The corresponding Hammett substituent constants, activation parameters, and primary deuterium isotope effects, suggest that the anti elimination from (19b) (for which p = 2.4 0.1, H/ D = 2.7 0.3, A/H = 12.5 0.2 kcal mol-1, and A= —31.0 0.6eu) proceeds to (20) via a more symmetrical transition state with a smaller degree of proton transfer, less charge development at the jS-carbon and greater extent of triple bond formation than for syn elimination from (19a) (for which p = 1.4 0.1, kn/kn = 7.8 0.3, AH = 8.8 0.1 kcal mol 1 and A= -23.6 0.4 eu). 

The photochemistry of benzaldehyde (90% 13C=0), 519, deoxybenzoin (99%) 13C=0), 521, and / -chloro benzoin (99% 13C=0), 522, in cyclohexane-Dn solution has been studied633 by spectroscopic techniques, such as XH chemically induced dynamic nuclear634 or electron polarization635 (CIDNP/CIDEP) or dynamic nuclear polarization636 (DNP). In all these cases the formation of benzaldehyde-D with emissive 13C=0 polarization has been observed and the results rationalized by intermolecular hydrogen (deuterium) abstraction by the photoexcited ketones from the solvent molecules and by reactions of cage-escaped radicals (equations 303-308), Benzoin, 520, is formed also. 

The proton on the ethenyl-CH group in ethenyl phenyl tellurium is replaced by lithium upon treatment with lithium dialkylamides in THF or diethyl ether at temperatures between — 20° and — 70". The 1-lithio-l-ethenyl phenyl tellurium reacted with deuterium oxide, benzaldehyde, and diphenyl ketone as expected1. 

Bis(phenylselanyl)methyllithiums 429 (R = H) are stable till 0 °C and were initially trapped with deuterium oxide, methyl iodide and benzophenone639. a-Substituted organolithium intermediate 429 (R = Me, w-CgH ), prepared with LiTMP in THF/HMPA at — 20 °C, reacted with alkyl bromides, ethylene oxide and benzaldehyde to give products 430 in good yields (Scheme 113)640. Bis(methylselanyl)methyllithiums 431 have been allowed to react with different electrophiles to afford products 432 (Scheme 113)640. Alkylated products have been deprotected with mercury(II) chloride or copper(II) chloride/copper(II) oxide, and by oxidation with hydrogen peroxide or benzeneseleninic anhydride644. Deprotection of selenoacetals to ketones can also be performed with sulfuric acid645. 

The cavity of p-CD, with a diameter of about 7 A, provides an attractive binding site for the substrate on the side of the primary OH groups. Benzaldehyde enclosed in the hydrophobic cavity of a thiamine-functionalized p-CD was first converted to a thiazolium adduct having a similarity to a cyanohydrin (Figure 4). This adduct readily formed a benzylic anion, as evidenced by fhe anion s characteristic reactions such as deuterium exchange and oxidation. 

Pyridine V-oxides may be deprotonated to give ylides which react with electrophiles such as carbon dioxide and ketones. For example, 4-chloropyridine /V-oxide reacts with butyllithium at -65 °C followed by quenching with carbon dioxide to give 4-chloropyridine A -oxide 2-carboxylic acid in 49% yield. Quinuclidine yV-oxide can be deprotonated with r-butyllithium to give the anion which can be trai ied with deuterium oxide or benzaldehyde. ... 

Reduction of the propargylic cation is observed upon reaction of y-benzylprotected-a -hydroxy complexes. A hydride shift from the benzyl group to the intermediately formed carbocation is observed. For example, deuterium-labeled complex (151) gave alkyne (152) with a deuterium in the a-position (Scheme 220). Benzaldehyde is observed as the side product. 

Gajewski has examined the secondary deuterium isotope effects in the addition of allyllithium and allyl Grignard additions to benzaldehyde [157]. With allyl-lithium and allylmagnesium halides a normal secondary deuterium isotope effect was observed. The results indicate that rate-determining single-electron transfer occurs with the allyl reagents. 

Thus, the reaction with aromatic aldehydes is second order in aldehyde and first order in hydroxide ion,31 and no deuterium becomes attached to carbon in the alcohol fragment when the reaction is carried out in deuterium oxide solution.32 It is interesting that when the reaction is carried out with benzaldehyde in the cold and in the absence of excess alkali, benzyl benzoate has been isolated.33 Although the point has not yet been settled, it seems probable that the ester is formed by a secondary reaction between the benzylate ion which is formed initially (XXIII) and two molecules of benzaldehyde 2M0... 

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