Subject transannular

By using various trapping reagents, it has been deduced that the transannular fragmentation is rapidly reversible. The cyclization of the fragmented radical C is less favorable, and it is trapped at rates which exceed that for recyclization under most circumstances. " Radicals derived from ethers and acetals by hydrogen abstraction are subject to fragmentation, with formation of a ketone or ester, respectively. 

The mechanism of the dehydrogenative transannular ring closure of cycloocta-tetraene in the presence of various inorganic reagents to provide complexes of pentalene has been the subject of debate... 

When subjected to the action of propanethiol under basic conditions (pH 9.2), jatrophone (2) undergoes a Michael reaction across its C8-C9 double bond, followed by facile transannular cyclization to give the tetracyclic diketone 3.2,9 The susceptibility of this enone part structure to conjugate addition has been proposed to constitute the event responsible for the pronounced biological activity of 2.9... 

However, this restriction does not hold if the phosphazene ring is subjected to ring-strain by the presence of a transannular ferrocenyl group, as in structure 3.37 and reaction (13).26 Under these circumstances, polymerization takes place to give 3.38 even if no halogen atoms are attached to the phosphorus atoms, although the reaction is accelerated by the presence of catalytic quantities of (NPC12)3. 

Oxidation of 2,3-cycloheptenoindole (184) over platinum provides the lactam (185) which undergoes a transannular condensation when subjected to chromatography on alumina, giving 7,8,9,10-tetra-hydrophenanthridone.206... 

Under Simmons-Smith conditions, bis-dihydropyran 566 was smoothly cyclo-propanated but 570 was also subject to transannular reactions under certain con-... 

The synthetic approaches to gf z-dinitro-g( z-bis(difluoroamino)octahydrodiazocines 105, key intermediates for the synthesis of explosives and solid propellant oxidizers, are outlined in Scheme 19. In the first approach, ketone 98 was subjected to a sequence of transformations to give oxime 101c in 40% overall yield. The 1,3-dioxolane protection of the keto functionality in the latter oxime was employed to avoid transannular reactions and, under these conditions, smooth conversion of oxime 101c to the corresponding gm-dinitro derivative 102c took place in moderate yield (36%). 

Neat A-(l -methyl-4-pentenyl)hydroxylamine underwent facile cyclization to the corresponding Y-hydroxypyrrolidine 1 on wanning briefly to 50- 60 °C, via a radical chain reaction involving the nitroxide radical. A-(l-Methyl-5-hexenyl)hydroxylamine cyclized to give A-hydroxypipe-ridine 2 only in refluxing xylene under high dilution conditions, this is necessary to avoid formation of byproducts. The cyclization was facilitated by the presence of a-methyl substituents in the hydroxylamine. Transannular cyclization of A-[(3-cyclohexenyl)methyl]hydroxylamine was not successful. Since the isolation of pure samples of the water-soluble and easily oxidized hydroxylamines was not a satisfactory procedure, the crude reaction mixtures were subjected to reduction with a zinc/acetic acid/acetic anhydride system to isolate acetylated cyclic amines. 

Curci et al. subjected cyclodecyne 125 to epoxidation with methyl(trifluoromethyl)dioxirane and observed a mixture (7 1) of m-bicyclo[5.3.0]decan-2-one 126 and m-bicyclo[4.4.0]decan-2-one 127, these products presumably arising via respective 1,5- and 1,6-transannular insertion pathways into the intermediate oxirene (Scheme 62) <1992TL7929, 1996CHEC-II(1)145>. Prior to this report, Concannon and Ciabattoni had observed the product profiles arising from the oxidation of several cycloalkynes with MCPBA (Table 18) <1973JA3284>. 

This chapter is concerned with the above-mentioned three problems of general interest, because transannular phenomena are the subject of a separate chapter. 

G. Mehta and co-workers unexpectedly encountered a novel transannular Cannizzaro reaction when 1,4-bishomo-6-seco[7]prismane dialdehyde derivative was subjected to basic conditions to yield a novel octacyclic lactone. " The transannular Cannizzaro reaction is the result of the proximity of the two reacting aldehyde groups induced by the rigid caged structure. 

Sesquiterpenes with eleven carbon atoms in the ring, for example humulene, have been subjected to electrophilic reactions providing products of transannular cyclization. 

Today, Supramolecular Chemistry would be unthinkable without the structural building blocks of cyclophanes. Nevertheless, traditional subjects attached to cyclophanes such as molecular strain, transannular interactions and other things are still of current interest. 

Deslongchamps and co-workers approach to the synthesis of Kempane diterpenes employed a ring-closing metathesis strategy in the construction of the 13-membered ring carbocycle, which was subsequently subjected to a transannular Diels-Alder reaction to produce the tricyclic... 

Diels-Alder reaction of a series of macrocycles of E,E-dienes with excellent enantiostereocontrol and diastereo-control. This was applied in the synthesis of 11,12-diace-toxydrimane by the transannular Diels-Alder reaction of 24 under the catalysis of the oxazaborolide catalyst to give 25 (Scheme 20.8). It was subjected to the Tamao oxidation and... 

Transannular aldolization is a powerful method for creating two new rings with at least two new stereogenic centers. Chandler and List reported on an enantioselective version of transannular aldolization of cyclic diketone catalyzed by proline derivative 87. 1,4-Cyclooctadione 86 was subjected to the intramolecular aldol reaction in the presence of /ra 5-4-fluoroproline 87 to give the transannular aldol product, (3-hydoxy ketone 88, in 84% yield with 96% ee (Scheme 27.15). In this reaction, proline catalyst bearing a substituent at the 4-position was effective for increasing enantioselectivity. The polycyclic product of 88 was further elaborated into (-l-)-hirustene 89, which is a... 

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