Intramolecular transfers

Rice S A 1981 An overview of the dynamics of intramolecular transfer of vibrational energy Adv. Chem. Phys. 47 117-200... 

Lithiated indoles can be alkylated with primary or allylic halides and they react with aldehydes and ketones by addition to give hydroxyalkyl derivatives. Table 10.1 gives some examples of such reactions. Entry 13 is an example of a reaction with ethylene oxide which introduces a 2-(2-hydroxyethyl) substituent. Entries 14 and 15 illustrate cases of addition to aromatic ketones in which dehydration occurs during the course of the reaction. It is likely that this process occurs through intramolecular transfer of the phenylsulfonyl group. 

Nadeau LJ, Z He, JC Spain (2003) Bacterial conversion of hydroxylamino aromatic compounds by both lyase and mutase enzymes involves intramolecular transfer of hydroxyl groups. Appl Environ Microbiol 69 2786-2793. 

Compounds such as phenylacetate esters and phenylethyl ethers, which have oxygen substituents that can serve as directing groups, show high ortho. para ratios under these conditions.12 These reactions are believed to involve coordination of the N02+ at the substituent oxygen, followed by intramolecular transfer. 

Fig. 6 An intrinsic molecular switch positioned in an STM tunnel junction. Here, the mechanism of intramolecular switching is independent of the surface. It is the intramolecular transfer of two protons which is supposed to shift the molecular orbitals of molecule since one phenyl is bonded to a sulfur atom. The protons transfer is triggered by the tip to surface electric field...

An intramolecular transfer of hydrogen as well as ring closure occurs with diazonium salts containing a suitably located second aromatic ring.87 The amount of ring closure by radicals, however, is very much less than the amount that occurs in the corresponding polar reaction. 

Reactions between bis(alkinyl)dimethylplumbanes and trialkylboranes resulted in the cleavage of the lead-alkinyl bond and the fast intramolecular transfer of the alkinyl group to the boron atom forming the alkinylborate anion and the triorganolead cation (structure A) (Figure 49)154. 

The other major approach toward overcoming the "alkyl transfer" difficulty of the Abramov reaction involves the use of silyl esters of the trivalent phosphorus acids. Unlike carbon, silicon does not have the stereochemical restraints associated with ordinary alkyl groups for intramolecular transfer.211 The preparation of mixed alkyl—silyl esters of trivalent phosphorus acids paved the way for the Abramov reaction to be of general utility.204 208 212 An example is shown in Equation 3.14. 

Directed intramolecular transfer hydrogenations are catalyzed by rhodium complexes with the pendant alkene acting as an internal sacrificial olefin (Equation (39)). 

The production of these branches is ascribed to intramolecular transfer, i.e., back-bite. CH2 —CH, CH. — CH,... 

Interestingly, reaction of alkynyl disilane 14 with trityl cation did not result in the formation of stable vinyl cations. Obviously, the formation of the four-membered disilacyclobutane ring is unfavorable. Similarly, treatment of alkyne 15 with the pre-formed triethylsilylarenium ion 1 derived from toluene did not give the expected intramolecular transfer of the silylium ion to the triple bond. Instead, only a complex product mixture was obtained. 

The reduction of a-allenic alcohols with lithium aluminum hydride afforded 1,3-dienes 376 via the intramolecular transfer of hydride from aluminum to the central carbon atom of the allene moiety [172]. 

A rather different allene cyclization that takes place in tandem with an alkylative process has been described by Trost and Urabe [66] (Eq. 13.52). Exposure of ketoal-lene 169 to divinylmethylaluminum 170 in dichloromethane solution leads to 171 in 60% yield. The mechanism of this alkylative cyclization involves complexation of the Lewis acidic aluminum to the carbonyl oxygen atom, followed by ring closure, leading to zwitterion 172. Intramolecular transfer of a vinyl group from aluminum to carbon completes the process. 

Rice, S. A. (1981), Overview of the Dynamics of Intramolecular Transfer of Vibrational Energy, Adv. Chem. Phys. 47, 117. 

Although electron transfers in biological systems are generally expected to be non-adiabatic, it is possible for some intramolecular transfers to be close to the adiabatic limit, particularly in proteins where several redox centers are held in a very compact arrangement. This situation is found for example in cytochromes C3 of sulfate-reducing bacteria which contain four hemes in a 13 kDa molecule [10, 11], or in Escherichia coli sulfite reductase where the distance between the siroheme iron and the closest iron of a 4Fe-4S cluster is only 4.4 A [12]. It is interesting to note that a very fast intramolecular transfer rate of about 10 s was inferred from resonance Raman experiments performed in Desulfovibrio vulgaris Miyazaki cytochrome Cj [13]. 

In less repetitive syntheses, it is possible to use remote functional groups as "control elements", a technique which depends more upon the opportunist tactics developed in the course of a synthesis rather than of a premeditated strategy. Such is the case, for instance, of the synthesis of strychnine (i) by Woodward [2], in which after synthesising the intermediate 2 a hydrogen at C(8) must be introduced onto the P-face (4), i.e., onto the most hindered concave face of the molecule (Scheme 8.1). Usually the reduction with a metal hydride would lead to the a-C(8)-H isomer (i.e., the hydride ion will atack from the less hindered face of the molecule), however in the present case the P-OH group at C(21) acts as a control element and, besides the reduction of the amide at C(20), a hydride ion attacks at C(8) from the P-face by an intramolecular transfer of the complex C(21)-0-Al-H (3). 

A simpler example of this kind of stereochemical control is the cyclopropanation of cyclopenten-2-ol (5) by the Simmons-Smith reagent in which the cij-biciclo[3.1.0]hexan-2-ol (7) is the diastereomer exclusively formed. As in the case of the hydrogen in strychnine, the methylene enters stereoselectively by intramolecular transference from an intermediate complex ( . 

As we showed previously in this chapter, silicon easily expands its valence shell to become a penta-coordinated species. Therefore, it is expected that an intramolecular transfer of organosilicon group from X to Y may occur via a radical mechanism, provided that the R substituents on the silicon atom are not good leaving groups (Reaction 6.20). 

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