Secondary carbon centers

The major application of the Mitsunobu reaction is the conversion of a chiral secondary alcohol 1 into an ester 3 with concomitant inversion of configuration at the secondary carbon center. In a second step the ester can be hydrolyzed to yield the inverted alcohol 4, which is enantiomeric to 1. By using appropriate nucleophiles, alcohols can be converted to other classes of compounds—e.g. azides, amines or ethers. 

There is evidence, both experimental and theoretical, that there are intermediates in at least some Sn2 reactions in the gas phase, in charge type I reactions, where a negative ion nucleophile attacks a neutral substrate. Two energy minima, one before and one after the transition state, appear in the reaction coordinate (Fig. 10.1). The energy surface for the Sn2 Menshutkin reaction (p. 499) has been examined and it was shown that charge separation was promoted by the solvent.An ab initio study of the Sn2 reaction at primary and secondary carbon centers has looked at the energy barrier (at the transition state) to the reaction. These minima correspond to unsymmetrical ion-dipole complexes. Theoretical calculations also show such minima in certain solvents, (e.g., DMF), but not in water. "... 

First, one had to check that the mechanism of action was correct. The product of co-ozonlysis of O-methyl-2-adamantanone oxime with 1,4-cyclohexanedione afforded on treatment with ferrous acetate a secondary carbon-centered free radical that was trapped with the usual spin trap, 2,2,6,6-tetramethylpiperidine-Ar-oxide (TEMPO), and involved a /3-scission of the adamantane fragment, thus proving that the attack of the Fe(ll) species occurred on the less-hindered peroxide bond oxygen atom (Scheme 85) <2004NAT900, 2005JOC513>. 

While homocuprates readily undergo substitution reactions at primary positions, they do not couple well with unactivated secondary halides. However, cyanocuprates undergo substitution reactions even at unactivated secondary carbon centers. ... 

TABLE 4. Rates and selectivity parameters for the nucleophilic reactions of anilines at cycloalkyl secondary carbon centers (c-(CF I2) lCHOSOiCfdLZ) in MeCN at 65.0 °C53... 

Alkyl radicals have been used to abstract hydrogen atom from C-H bonds at secondary carbon centers. For instance, Fuchs has developed a self-immolative elimination of aryl sulfones [84]. The or/Ao-silylated sulfone gives upon treatment with tin hydride and AIBN a primary alkyl radical that abstracts a hydrogen atom in a... 

The bis-E ck. cyclization of trienyl iodides has been applied as a key reaction by Overman to total syntheses of stemodane diterpenes and scopadulcic acid. Treatment of the 6R, %R epimer of the trienyl iodide intermediate 259 with Pd(dppb) in the presence of Ag2C03 in DMA provided two tricyclic products 260 (40 %) and 261 (25 %). The major product 260 has the stemodane skeleton [110]. On the other hand, w-cyclization of the 65, 8i epimer of the trienyl iodide 262 proceeded with complete stereo- and regioselectivity as shown by 263 and 264 to afford the tricycle of the scopadulan skeleton 266, from which total synthesis of scopadulcic acid A (267) was achieved. In the second cyclization as shown by 264, generation of the cyclohexylpalladium intermediate 265, having Pd attached to the secondary carbon center is favored to give 266 selectively. Formation of a stemodane skeleton is expected from the 6R, %R epimer [111]. 

The 1,2-addition of dialkylzinc reagents, in particular Et2Zn, to aryl imines is stereocontrolled by a ligated form of copper bearing a hemi-labile, monophosphine oxide (Me-DUPHOS(O), Nonracemic secondary carbon centers bearing a... 

Semipinacol rearrangement events were first defined as a special type of pinacol rearrangement by Tiffeneau in 1923. In Tiffeneau s original conception, these reactions involved migration toward the secondary carbon center on a tertiary/secondary diol as shown in Scheme 1.9 (58 59), the reverse regiochemistry of the typical pinacol rearrangement. 

In contrast, ring-opening of the cw-fused analog demonstrates only a slight preference for the formation of the secondary carbon-centered radical (51 49) from the intermediate dioxanyl radical (eq27). 

Treatment of a,ot-dialkyl substituted phosphonoesters (377) with LiAlH4 caused the one-pot reduction of the ester moiety followed by dephosphorylation to yield the corresponding primary alcohols (378) bearing a controllable jS secondary carbon center (Scheme 132). ... 

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