Primary position

Regioselective Acylation of Hydroxy Compounds. AUphatic diols can be selectively acylated at the primary position by a number of Upases in nonaqueous solvents. For example, PPL suspended in solutions of various diols in ethyl carboxylates catalyzes transesterification in a highly regioselective manner, producing primary monoesters in up to 97% yield (93). Similarly, chloramphenicol [56-75-7] (72) (R = NO2) can be acylated by a number of Upases to produce optically pure, water-insoluble 3-0-palmitate in a highly selective manner (94). 

Free radicals may also react with a hydrocarbon molecule from the feed by abstracting a hydrogen atom. In this case the attacking radical is terminated, and a new free radical is formed. Abstraction of a hydrogen atom can occur at any position along the chain. However, the rate of hydrogen abstraction is faster from a tertiary position than from a secondary, which is faster than from a primary position. 

Abstraction of a hydride ion from a tertiary carbon is easier than from a secondary, which is easier than from a primary position. The formed car-bocation can rearrange through a methide-hydride shift similar to what has been explained in catalytic reforming. This isomerization reaction is responsible for a high ratio of branched isomers in the products. 

Thus, the process of hydride ion abstraction from a primary position is approximately thermoneutral, and hence we must conclude that it is an energetically allowed process, although possibly with a relatively small reaction rate. A process competing with primary H abstraction (Reaction 13) is methide ion abstraction (Reaction 11, loss of CH4 from the... 

Neither methyl nor ethyl fluoride gave the corresponding cations when treated with SbFs. At low temperatures, methyl fluoride gave chiefly the methylated sulfur dioxide salt, (CH3OSO) ShF while ethyl fluoride rapidly formed the rert-butyl and ferf-hexyl cations by addition of the initially formed ethyl cation to ethylene molecules also formed ° At room temperature, methyl fluoride also gave the tert-butyl cation. In accord with the stability order, hydride ion is abstracted from alkanes by super acid most readily from tertiary and least readily from primary positions. 

Hattori Y, Levi R Effect of PGDj on cardiac con- 43 tractihty a negative inotropism secondary to coronary vasoconstriction conceals a primary positive inotropic action. J Pharmacol Exp Ther 1986 237 ... 

Selective removal of one isopropylidene group from a diacetal may be achieved by a variety of procedures, most of them involving protic or Lewis acids.100 Particularly common is the hydrolysis of the acetal engaging of the primary position of di-O-isopropylidene derivatives. Bhaskar et al,101 studied the selective deprotection of di-O-isopropylidene acetals derived from D-glucose, D-xylose, and D-mannose, using acid zeolites and montmorillonite K-10. When 102 was submitted to acid hydrolysis in aqueous methanol, the best yields (85—96%) for the monoacetal 105 were obtained when H-beta and HZSM-5 zeolites were employed as catalysts (Scheme 24, Table IV). HY zeolite proved to be ineffective, whereas the yield obtained for the montmorillonite K-10-catalyzed reaction was low (22%). The zeolites found most effective were then used for the hydrolysis of the diacetal 103 and 104, providing excellent yields for the desired corresponding monoacetals 106 and 107. 

These differences in the course of the reaction of Grignard and sodium compounds are not limited to carbonations but are also observed in carbonyl addition reactions. Whereas cinnamylmagnesium bromide always reacts at the secondary carbon atom next to the benzene ring, the sodium compound may react at either the secondary or the primary position, depending on the electrophilic reagent.403... 

Aroyl migrations towards primary positions have been observed during the acid-catalyzed removal of acetal groups from 1,2,3,5-tetra-0-benzoyl-4,6-0-ethylidene-D-glucitol587 and 2,4-0-ethylidene-l,3-di-0-(p-nitrobenzoyl)erythritol.588... 

The phosphate of ethylene glycol must derive from the ribitol phosphate moiety, which consequently is phosphorylated at a primary position, assumed to be 0-5 of (pro-D)-ribitol for biosynthetic reasons. In the proposed structure for the S10A repeating-unit (14), the anomeric natures of the sugar residues were not determined. The optical rotations of S10A and the hexasaccharide, [a]D +12° and +11°, respectively, indicate that they contain both a- and /3-D-linked sugar residues. 

Rp is an exponent that describes the relationship of a primary isotope effect with H in the secondary position to a primary isotope effect with D in the secondary position. Rs is an exponent that describes the relationship of a secondary isotope effect with H in the primary position to a secondary isotope effect with D in the primary position. According to the Rule of the... 

When secondary Grignard reagents are used, the coupling product sometimes is derived from the corresponding primary alkyl group.169 This transformation can occur by reversible formation of a nickel-alkene complex from the cr-bonded alkyl group. Reformation of the cr-bonded structure will be preferred at the less hindered primary position. 

Under non-aqueous conditions the epoxy function in the epoxylactones can be opened only by Lewis acid assistance. Thus, 2-fluoro-2-deoxy-lactones have been prepared from 2,3-epoxylactones by treatment with HF-amine complexes [38,49,50], while 5,6-epoxylactones yield 6-deoxy-6-fluoro-lactones by this treatment [49, 50]. Likewise, BFj-assisted opening of a 2,3- epoxy function with TMSN3 [51] gave a 2-azido-2-deoxy-lactone [52]. In all cases the opening of the epoxide is a frans-opening, and it is noteworthy that under acidic conditions the nucleophile attacks at C-2 or at the primary position, similar to the opening of acetoxonium ions by bromide ions in the... 

DNA Amplification Kit as well as the PCR cloning check. The plasmids with appropriate end-sequences are selected (one clone for one gene) and re-arrayed to their primary positions in a 96-well format. 

Although the use of N,N-dimethylformamide permits satisfactory chlorination or bromination of primary positions at room temperature, side reactions can occur between carbon tetrahalides, triphenylphosphine, and JV,N-dimethylformamide that can, in some cases, result in low yields of halogenated products (see also, Section II, 2c p. 230). 

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