At alpha carbon

From a stereochemical viewpoint, the sulfur extrusion methods12122 using P(NEt2)3 seem to have certain advantages, because chiral centers at alpha carbon atoms are not involved in the lanthionine formation. However, due to the possible formation of ionic intermediates prior to formation of the sulfide bridge, undesired symmetrically substituted or also ste-reochemically undesired lanthionines may inadvertently be formed. Possible solutions to circumvent these problems have also been reported. 23,26 ... 

The carbon-carbon double bond is the distinguishing feature of the butylenes and, as such, controls their chemistry The carbon-carbon bond, acting as a substitute, affects the reactivity of the carbon atoms at the alpha positions through the formation of the allylic resonance structure. This structure can stabilize both positive and negative charges. Thus allylic carbons are more reactive to substitution and addition reactions than alkane carbons. Therefore, reactions of butylenes can be divided into two broad categories (J) those that take place at the double bond itself, destroying the double bond and ( 2 > those that take place at alpha carbons. 

Amines Hardly detectable in case of acyclic aliphatic amines high intensity for aromatic and cyclic amines Beta cleavage yielding >C=Nv base peak for all 1° amines at m/e = 30 (CH2=N+H j moderate M-1 peak for aromatic amines loss of 27 (HCN) in aromatic amines fragmentation at alpha carbons in cyclic amines... 

But that is not the case. What the Korean lab found out was that when this procedure is performed, the OH stabilizes on the alpha carbon. That is the carbon right next to the phenyl ring. If one has any use for it as is then that is fine. But what is most preferable is to reduce the OH to get the propenylbenzene (say isoelemicin for our example). Using the simple potassium bisulfate reduction recipe, one can get rid of the OH with no problems at all. 

With Phenylpropanolamine at hand (or ephedrine and pseudo-ephedrine) one would next need to reduce that alpha carbon OH group to get the final amine. Strike understands that the current favorite methods for doing this involve lithium and amine. HI and red P or other iodine related protocols. So when you meth heads ruin every aspect of those methods as well, what will you do then The following are a couple of OH reduction methods (Strike thinks) that have applicable use [99-100]. 

Saturated ring systems lose side chains at the alpha carbon. Upon fragmentation, two ring atoms are usually lost. 

As a class of compounds, the two main toxicity concerns for nitriles are acute lethality and osteolathyrsm. A comprehensive review of the toxicity of nitriles, including detailed discussion of biochemical mechanisms of toxicity and stmcture-activity relationships, is available (12). Nitriles vary broadly in their abiUty to cause acute lethaUty and subde differences in stmcture can greatly affect toxic potency. The biochemical basis of their acute toxicity is related to their metaboHsm in the body. Following exposure and absorption, nitriles are metabolized by cytochrome p450 enzymes in the Hver. The metaboHsm involves initial hydrogen abstraction resulting in the formation of a carbon radical, followed by hydroxylation of the carbon radical. MetaboHsm at the carbon atom adjacent (alpha) to the cyano group would yield a cyanohydrin metaboHte, which decomposes readily in the body to produce cyanide. Hydroxylation at other carbon positions in the nitrile does not result in cyanide release. 

The propensity of nitriles to release cyanide subsequent to metaboHsm is the basis of their acute toxicity. Nitriles that form tertiary radicals at their alpha carbon atoms (eg, isobutyronitrile, 2-methylbutyronitrile) are substantially more acutely lethal than nitriles that form secondary radicals at their alpha carbons (eg, butyronitrile, propionitnle). Cyanohydrins are acutely toxic because they are unstable and release cyanide quickly. Alpha-aminonitriles are also acutely toxic, presumably by analogy with cyanohydrins. 

Substitution Reactions. The chemistry at alpha positions hinges on the fact that an aHyUc hydrogen is easy to abstract because of the resonance stmctures that can be estabUshed with the neighboring double bond. The aHyUc proton is easier to abstract than one on a tertiary carbon these reactions are important in the formation of alkoxybutenes (ethers). 

AEyl chloride reacts with sodamide in Hquid ammonia to produce benzene when sodamide is in excess, hexadiene dimer is the principal product, with some trimer and tetramer (C24, six double bonds). AEylation at carbon atoms alpha to polar groups is used in the preparation of a-aEyl-substituted ketones and nittiles. Preparation of P-diketone derivatives, methionic acid derivatives, and malonic ester, cyanoacetic ester, and P-keto-ester derivatives, etc, involving substitution on an alpha carbon between two polar carbonyl groups, is particularly facEe. 

And diis meant that die chain could turn corners only at die alpha carbons.. .. I creased die paper in parallel creases dirough the alpha carbon atoms,. so that I could bend it and make die bonds to the alpha carbons, along die chain, have tetrahedral value. And then I looked to see if I could form hydrogen bonds from one part of the chain to the next. He. saw diat if he folded die. strip like a chain of paper dolls into a helix, and if he got die pitch of the screw right, hydrogen bonds could be shown to form,... 

Nitrophenyl)ethyl Carbamate. The photolytic removal of this group occurs twice as fast as does the 2-nitrobenzyl carbamate. Additionally, substitution at the alpha carbon increases the rate of cleavage even more. 

This excellent regiocontrol was exploited by subjecting terminal alkenes and hydroxyalkynoates to ruthenium catalysis conditions to afford butenolides and pentenolides (Equation (23)).36 The Alder-ene reaction occurs preferentially to form the G-G bond at the alpha-carbon of the alkynoate. The unusually high regioselectivity is attributed to a synergistic effect derived from an enhanced coordination of the hydroxyl group to the ruthenium. 

Saturated rings with side chain lose side chain at the alpha carbon atom and positive charge remains with the ring. 

A variety of radical products is observed following gamma radiolysis of the N-acetyl amino acids at 77 K (6), depending on the nature of the side chain of the parent amino acid. In the case of N-acetyl alanine, for example, the intermediates are (i) the anion radical IV (ii) the decarboxylation radical V (iii) the deamination radical VI and (iv) the alpha carbon radical VII. 

A similar behaviour has been found to occur with the other N-acetyl amino acids. In each case, the most stable radical observed at 303 K was the alpha carbon radical, as was also observed for the aliphatic carboxylic acids. In Table VI the radical yields observed following gamma radiolysis of a series of N-acetyl amino acids at 303 K are reported, together with the stable radical intermediates observed at this temperature (5). 

POLYAMINO ACIDS Aliphatic polyamino acids irradiated in the solid state have been reported to undergo N-Ctf, main-chain, bond scission on gamma radiolysis (9) and the stable radical intermediates formed following radiolysis at 303 K are alpha carbon radicals, as observed in the N-acetyl amino acids. 

Two stable radical intermediates are observed following gamma radiolysis at 303 K. The alpha carbon radical VIII and the side chain radical IX are formed in approximately equal yields, with the total G-value for radical production equal to 3.2. This value is similar to that observed for the poly acids. The observed radicals are those which would be expected on the basis of the aliphatic carboxylic acids and previous studies of the poly amino acids with aliphatic side chains. 

The first report of this new type of kinetic isotope effect in a Menshutkin reaction was published by Matsson and coworkers in 198744. In this study, the alpha carbon kll/ku kinetic isotope effect was measured for the Menshutkin reaction between N,N-dimethyl-para-toluidine and labelled methyl iodide in methanol at 30 °C (equation 35). The carbon-11 labelled methyl iodide required for this study was prepared from the nC atoms produced in the cyclotron in three steps45 (equation 37). 

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