Dyotropic rearrangements, and

Dyotropic Rearrangements and Related o--cr Exchange Processes, 16, 33 Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8, 167 Fischer-Tropsch Reaction, 17, 61 Flurocarbon Derivatives of Metals, 1, 143... 

Dyotropic rearrangements are uncatalyzed concerted dihydrogen exchange reactions, another class of orbital symmetry controlled processes, which involve the simultaneous migration of two cr-bonds. These conversions can be both thermal and photochemical. They can be subdivided into two types (1) reactions in which two migrating cr-bonds interchange their positions (equation 78), and (2) reactions without such positional interchange (equation 79)91,92. 

Furthermore, a brief review of dyotropic rearrangements starting with the hypothetical transformations of 1,2-disubstituted cyclobutenes was published98 in which two types of these processes were described and a general theory covering such rearrangements was outlined. Quantum chemical calculations of the reaction barrier for the dihydrogen... 

An irreversible dyotropic rearrangement of fluoro-substituted tris(silyl)hydroxyl-amines (127) (128) has been reported and ab initio and density functional calculations for model compounds have confirmed the dyotropic course of this rearrangement. ... 

Dyotropic rearrangement is an uncatalysed process in which two a bonds simultaneously migrate intramolecularly by a dyotropic transition state 202 and has been observed in organosilylhydroxylamine derivatives 201 (equation 59). 

To explore the dyotropic rearrangement of silyl hydroxylamines, Schmatz, Klinge-biel and colleagues studied the behaviour of 0-lithium-Af,Af-bis(f-butyldimethylsilyl) hydroxylamine 207 in the presence of chlorotrimethylstannane (equation 62). They found that the primarily formed Af,Af-bis(f-butyldimethylsilyl)-0-(trimethylstannyl)hydroxyl-amine 208 underwent a dyotropic rearrangement to form 209. This reaction mechanism is corroborated by quantum chemical calculations partly employing an effective core potential for tin. 

Migration of a substituent on a disilene giving the corresponding silylene [pathway (3)] should be considered as a pathway for the /AZ-isomerization but occurs usually with much higher activation energies than pathways (1) and/or (2). The pathway (3) and related dyotropic rearrangement are discussed in detail in Section IV.A.3. 

Dyotropic rearrangements are defined as the uncatalyzed concerted rearrangements in which two groups migrate intramolecularly and exchange positions (equation 1). Although... 

Danheiser and coworkers described a convenient preparation of oxetanones via the condensation of thioester lithium enolates with carbonyl compounds and subsequent lac-tonization under proper conditions592. The asymmetric version was reported later593, the configuration of the new chiral center being established by a stereospecific dyotropic rearrangement to the y-butyrolactone (Scheme 125)594. 

The initiating reaction step of decomposition in path (a) of Eq. (56) consists of an isomerization of tran5-2-tetrazene into tra 5-l-tetrazene, which, with a-elimination of amine, produces azides [Scheme 6, Eq. (57), paths (a) and (b)]. The isomerization in path (a) [Eq. (57)] may also be the first reaction step toward transformation [Eq. (56), path (b)]. The next reaction step of trany-l-tetrazene (47), necessary for the formation of products according to Eq (56b), probably consists of an inversion according to path (c) of Eq. (57),or a dyotropic rearrangement [cf. ref. 54] as in... 

The fact that the decomposition of ionized methylpropene (106) at longer lifetimes is preceded not only by hydrogen randomization but also by participation of the C(2) carbon atom (indicated with an asterisk in Scheme 14) in the expulsion of ethylene has been explained by invoking the intermediate existence of methylcyclopropane (107) and 2-butene (108) (Scheme 14). This is in line with the finding that direct ionization of neutral methylcyclopropane gives 107 which is known to undergo ethylene loss. The isomerization sequence described in Scheme 14 can be viewed as a further example for a mass spectrometric dyotropic rearrangement ". ... 

This chapter provides a summary of the mechanistic methods applicable to dyotropic rearrangements. To date the most detailed studies have been carried out with organosilicon compounds. The presence of heteroatoms appears to be necessary. However, the present author believes that dyotropic processes are not restricted to these elements, cr-a exchange reactions—irrespective of the mechanism—involve far-reaching molecular transformations and are thus of potential synthetic interest (76). 

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