Cycloheptane synthesis

Cyanthiwigin synthesis 180 Cyclobutane synthesis 76, 102 Cycloheptane synthesis 53,165, 169, 180,... 

Electrocyclic closure of butadiene units encased within cycloheptane rings has been used to obtain bicyclo[3.2.0]heptene systems (Scheme 5)12. For example, irradiation of eucarvone 21 led to the formation of adduct 22 in 52% yield via a disrotatory ring closure123. This adduct was used as a key intermediate in the synthesis of the pheromone grandisol, 23, which proceeded in 20% overall yield from 22. In their synthesis of a-lumicolchicine. Chapman and coworkers utilized a photochemically initiated four-electron disrotatory photocyclization of colchicine to produce /Murnicolchicine 24a and its /-isomer 24b in a 2 1 ratio12b. These adducts were then converted, in a second photochemical step, to the anti head-to-head dimer a-lumicolchicine 25. 

Cycloheptane annelation.1 A new route to cycloheptanes is based on a Lewis acid-catalyzed, intramolecular addition of an allylsilane group to a 3-vinylcycloal-kenone (equation I). This annelation has been applied to a synthesis of the ses-... 

Synthesis, Stereochemistry and Transformations of Cyclopentane-, Cyclohexane-, Cycloheptane-, and Cyclooctane-Fused 1,3-Oxazines, 1,3-Thiazines, and Pyrimidines... 

The enthalpy of fomation of two such species has been measured, namely the cyclopropane and cycloheptane derivatives. The difference between the values for these two species, both as solids, is 238.1 kJmol . Is this difference plausible Consider the difference between the enthalpies of formation of the parent cycloalkanes as solids, 194 kJ mol . The ca 44 kJ mol discrepancy between these two differences seems rather large. However, there are idiosyncracies associated with the enthalpies of formation of compounds with three-membered rings and almost nothing is known at all about the thermochemistry of compounds with seven-membered rings. Rather, we merely note that a seemingly well-defined synthesis of cycloheptyl methyl ketone was shown later to result in a mixture of methyl methylcyclohexyl ketones, and superelectrophilic carbonylation of cycloheptane resulted in the same products as methylcyclohexane, namely esters of 1-methylcyclohexanecarboxylic acid. The difference between the enthalpies of formation of the unsubstituted alicyclic hydrocarbons cycloheptane and methylcyclohexane as solids is 33 kJmol . This alternative structural assignment hereby corrects for most of the above 44 kJ mol discrepancy in the enthalpies of formation of the two oximes. More thermochemical measurements are needed, of oximes and cycloheptanes alike. 

The reaction of 1,2-dicarbonyl compounds with amidrazones, semicarbazide, thiosemicarbazide and aminoguanidine has also been used for the synthesis of condensed 1,2,4-triazines. Cyclohexane-, cycloheptane- and cyclooctane-1,2-diones (489) with amidrazones (453) afford the cycloalkatriazines (490) (78HC(33)189, p.66l). 

Stereoselective synthesis of medium-sized rings was possible from compounds such as (77 Scheme 15),l0la which were readily derived from intramolecular cyclopropanations (see equation 18). Treatment of (77) with 1 equiv. of ethanethiol in the presence of a catalytic amount of zinc chloride generated the hemithioacetal (78), which in the presence of boron trifluoride etherate formed the cycloheptane system (79), in which the two carbonyls are differentiated. 

The following references contain additional examples of this method and corresponding reaction types Synthesis of 3-fluoroethyl-2-cyclopenten-l-ones [35], preparation of functionalized bicyclo[5.3.0]decane systems and conversion of 1,2-divinylcyclopropanes to functionalized cycloheptanes [36] e.g. karaha-naenone [37], ( )-/Thimachalene [38][39]. Metal-catalyzed ring expansions in which cyclopropane (e.g. [40] [41] [42] [43] [44]) or aziridines (e.g. [45] [46]) and diaziridines (e.g. [45]) function as essential moieties are well known reactions. 

Cycloheptane derivatives (7, 192-193). Wender et a/. have applied their cycloheptane annelation procedure to total syntheses of the pseudoguaianolides damsinic acid (1) and confertin (2). The paper describes the synthesis of 1-lithio-l-methyl-2-vinylcyclopropane, which is the annelation reagent utilized in the pseudo-guaianolide syntheses. 

Section 1.13.5 Miscellaneous reactions. Takeshita and coworkers reported the remarkable use of intramolecular ene reactions to form cycloheptanes and cyclooctanes. Pyrolysis of (216) in toluene at 200 C gives 97% of the cycloheptane (215). Reaction of (216) with SnCU in THF gives 85% of cyclooctane (217), which is an intermediate in the synthesis of cycloaraneosene. 

From another viewpoint, the value of the arene-alkene meta cycloaddition arises from its capacity to produce a cycloadduct (66 equation 14) with three new rings and up to six new stereocenters, an impressive feat even when compared with the highly regarded Diels-Alder cycloaddition. Moreover, the cycloadduct can be used in the synthesis of a variety of commonly encountei structural types including cyclopentanes, cycloheptanes, bicyclo[3.2.1]octanes and bicyclo[3.3.0]octanes. While fr uently overlooked in some discussions of reaction classification, the overall processes leading to cycloheptanes, bi-cyclo[3.2.1]octanes and bicyclo[3.3.0]octanes are clearly classifiable as [5C + 2C], [3C + 2C] and [3C + 2C] cycloadditions, respectively. Examples of these types will be given in the following section. 

The synthesis of 3,3,7,7-tetramethylcycloheptyne (64), a carbocyclic analogue of 55, has also been performed. The bishydrazone (63) derived from tetramethyl-cycloheptane-l,2-dione (62) was oxidized with lead tetraacetate and 64 was obtained together with 65, 66, 67 and 68. The last compound (68) is a dimer of 64 with... 

Cycloheptanes.—Two full papers have appeared on subjects mentioned in Vol. 1 Demole and Enggist s karahanaenone synthesis,and the irradiation of eucarvone. " Another paper concerning the irradiation of eucarvone has appeared in this case the substrate was protonated by carrying out the reaction in fluorosulphonic acid at — 78 °C. The products obtained after quenching the reaction with potassium carbonate in methanol are shown in Scheme 5, together... 

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