Cycloheptanes functionalized

Fig. 12.4. Vapor-to-water transfer data for saturated hydrocarbons as a function of accessible surface area, from [131]. Standard states are 1M ideal gas and solution phases. Linear alkanes (small dots) are labeled by the number of carbons. Cyclic compounds (large dots) are a = cyclooctane, b = cycloheptane, c = cyclopentane, d = cyclohexane, e = methylcyclopentane, f = methylcyclohexane, g = cA-l,2-dimethylcyclohexane. Branched compounds (circles) are h = isobutane, i = neopentane, j = isopentane, k = neohexane, 1 = isohexane, m = 3-methylpentane, n = 2,4-dimethylpentane, o = isooctane, p = 2,2,5-tri-metbylhexane. Adapted with permission from [74], Copyright 1994, American Chemical Society...

Chemical/Physical. Cycloheptane will not hydrolyze because it has no hydrolyzable functional group. 

The nitrone 127 (96% ee) containing an additional carbon atom was synthesized in a similar manner as 124. However, for nitrone 127, no spontaneous cyclization took place (Scheme 12.43). Upon heating of 127 in toluene, an inseparable mixmre of product isomers was formed. It was also found that in the presence of a stoichiometric amount of ZnCl2, the reaction proceeded to give the bicyclo[4.2.1] product 128 as the only observed product with close to complete retention of enantiopurity (ee=94%). The authors propose a more polarized transition state of the Zn-mediated reaction with a well-developed positive charge on one of the carbon atoms of the alkene moiety to account for the inverted direction of the regioselectivity of the reaction (230). A subsequent reduction gave the functionalized cycloheptane 129. 

Figure 7 G(Si) value as a function of the carbon atom numbers in the molecules. When more than one measured value was published, we tried to select the most probable value. Alkanes (1) propane, (2) w-butane, (3) w-pentane, (4) cyclopentane, (5) w-hexane, (6) cyclohexane, (7) w-heptane, (8) cycloheptane, (9) methylcyclohexane, (10) w-octane, (11) cyclooctane, (12) isooctane, (13) w-decane, (14) cyclodecane, (15) cw-decalin, (16) trawx-decalin, (17) w-dodecane, (18) dicyclohexyl, (19) n-hexadecane. (From Refs. 18, 29, 65, 92, 148, and 155.)...

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. 

Additionally, benzoannelated cycloheptanes 54 were obtained in good yields (Scheme 18). It was also possible to extend the methodology to dis-ubstituted or benzoannelated iodo arenes as substrates, giving rise to the formation of various functionalized annelated cyclohexanes and cyclohexanes 55-61 (Scheme 19). 

The cyclopropane system is a tool for inserting a methylene unit into a ring system to form a larger ring structure. Even densely functionalized pyranoids such as 161 [130,131] and cyclohexanes [132] expand into heptanoids and cycloheptanes, respectively. 1,2-C-dibromomethy-lene sugar 163 expands its pyranose ring to give oxepine 164 [133] (O Scheme 39). 

The present [3 + 4] annulation methodology for the synthesis of seven-membered carbocycles involves a straightforward procedure that also provides the product functionalities (e.g., masked and unmasked ketone carbonyl and trimethylsilyl groups) that can be transformed to hitherto inaccessible or difficult-to-prepare cycloheptane structures. The prior approach,7-9 based on Cope rearrangement of cis-1,2-divinylcyclopropane, bears an intrinsic drawback in that there exist a limited number of methods for stereoselective preparation of the substrate. 

No details were given so far about the structure of these compounds. One of the most interesting applications of the method could be the synthesis of enantiomerically pure, highly functionalized cycloheptane derivatives, since divinylcyclopropanes should be obtainable by the appropriate rearrangement of other primary products. 

Bocian DF, Strauss HL (1977) Vibrational spectra, conformations and potential functions of cycloheptane and related ox nes. J. Am. Chem. Soc. 99 2866... 

Thermal homo [1,5] hydrogen shifts have been used as a ring-expansion route to cycloheptane derivatives e.g. heating the bicyclic ketone (89) at 200°C for 2h caused isomerization to the cycloheptyl ketone (90). This route was used to prepare a functionalized hydroazulene. ° ... 

Ewing, M. B. Marsh, K. N. Excess functions for cyclopentane + cyclohexane, cyclopentane -t cycloheptane, and cyclohexane +... 

Siloxyallyl cations are comparatively reactive and electrophilic, and their cycloadditions proceed under mild reaction conditions and at low temperatures, being sufficiently reactive to be trapped by dienes. These conditions can accommodate various preexisting functionalities in the substrate molecule and thus exhibit a good potential and compatibility to be adapted to building cycloheptane substructures in complex natural product syntheses. These advantages merit the arguable extra step to prepare the enolsilanes for [4+3] cycloaddition reactions. 

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