Strained hydrocarbons, synthesis

The next four procedures describe the preparation of strained ring systems. Preparation of 3-CHLORO-2-(CHLOROMETHYL)-l-PROPENE provides a facile approach to the olefin required for the synthesis of [1.1.1 [PROPELLANE, one of the most strained hydrocarbons prepared to date. The ready availability of this hydrocarbon should prove particularly useful to those interested in the development of the chemistry of this fascinating compound. Preparation of N-BENZYL-2,3-AZETIDINEDIONE provides an efficient approach to the unadorned a-keto-/3-lactam, a potential... 

Efforts towards the synthesis of strained polycyclic hydrocarbons have been described. These compounds are of interest as fuels and fuel additives for advancedpropulsion. Chemistry has been devised for the attachment of azido functionality to the strained hydrocarbon nucleus. Highly unsaturated substituted cubanes have been synthesized. Ring-opening metathesis polymerization of basketene and 2,3-diazabicyclo[2.2.1]hept-2-ene has been studied. 

It is not unreasonable to expect preparatively useful photoreactions of appropriately functionalized dihalocyclopropanes also. Although the present trend in gew-dihalocyclopropane chemistry clearly favors the use of more highly functionalized substrates, the traditional role — mentioned in the introduction — of employing these strained molecules in hydrocarbon synthesis, is by no means an approach of the past. This point is stressed by the recent synthesis of octavalene... 

This desaturase transforms palmitic (C16 0) and stearic (Ci8 0) acids to palmitoleic (A9 C16 1) and oleic (A9 C18 i) acids, precursors of ct>7 and ct>9 fatty acids and 7- and 9-HC. Several desatl mutants have been described (Figure 4.3). The gene is expressed in both the fat body and oenocytes and plays a role both in general lipid metabolism and in hydrocarbon synthesis (Ueyama et al., 2005 Marcillac et al., 2005a Figure 4.4). A piggyBac strain inserted in... 

Metallacyclobutanes formed from cyclopropanes upon reductive elimination usually regenerate the starting material. Thus, reactions of this type are not useful in synthesis of new cyclopropanes. In some selected cases, however, strained hydrocarbons with cyclopropane subunits yield metallacyclobutanes which upon decomplexation give cyclopropanes not identical with the starting material. These conversions, however, are hard to generalize and often lead to unselective product formation. 

Dibenzo[2.2]paracyclophane-1,9-diene (2), a unique molecule with two parallel sets of mutually orthogonal aromatic rings, was first synthesized in 1985 by Wong et al. [18]. The reported five-step synthesis gave the strained hydrocarbon in only 0.5% yield. Later a more versatile and economic approach to dibenzoannelated [2.2]paracyclophanedienes 11 including the parent compound 2 was developed by de Meijere et al. [19]. The dibromo[2.2]paracyclo-phane-l-ene (6) and the tetrabromo[2.2]paracyclophane-1,9-diene (7) were obtained from commercially available [2.2]paracyclophane (1) in a bromination-dehydrobromination reaction sequence. With compounds 6 and 7 available in large quantities, the palladium catalyzed coupling with alkenes (Heck reaction)... 

The conversion of alcohols directly into the structurally related hydrocarbons by ionic hydrogenation can provide a means of synthesis for compounds that would be extremely difficult or impossible to obtain by other methods. A good example is the synthesis of 2-terr-butyladamantane (12, R = Me). This interesting, highly strained compound may be synthesized in moderate overall yield by a conventional multiple-step route.149 Alternatively, it is obtained in 90% isolated yield upon treatment of a dichloromethane solution of the readily available 2-/c/7-bulyI -2-adamantanoI (11, R = Me)150 and one equivalent of either tri-n-hexylsilane151152 or triethylsilane153 with trifluoroacetic acid at room temperature (Eq. 16). 

Reductive 1,3-elimination reaction of alkyl dihalides constitutes one of the classical methods for the preparation of cyclopropyl derivatives and is particularly useful for the synthesis of highly strained polycyclic hydrocarbons. A new preparation method of [l.l.ljpropellane, more versatile than the original Wiberg s method, has been devised3,4. Thus, treatment of l,l-dibromo-2,2-bis(chloromethyl)cyclopropane with alkyllithium or lithium powder affords [1.1. ljpropellane by two successive 1,3-eliminations of halogens by way of 1 -bromo-2-(chloromethyl)bicyclo[l. 1. Ojbutane (equation 1). This method has been... 

The application of this reaction to other ring systems has shown that the yield of the bicyclic hydrocarbon decreases as the strain involved in the product increases. For example, the mercury sensitized decomposition of bicyclo [3.2.0] heptanone-3 (XXIII) leads to very little of bicyclo [2.2.0] hexane and gives more of bicyclo [2.1.1] hexane than of bicyclo [2.2.0] hexane. The reaction has been successfully applied to the synthesis of a substituted bicyclo [2.1.0] pentane (XXVIII) from a sub-... 

Agranat, I., Suissa, M. R., Cohen, S., Isaksson, R., Sandstrom, J., Dale, J., and Grace, D. (1987) A novel titanium-induced aromatic dicarbonyl coupling. Synthesis of a chiral strained polynuclear aromatic hydrocarbon, J. Chem. Soc., Chem. Commun., 381-383. 

The cyclopropane synthesis is also suitable for the preparation of highly strained bicyclic hydrocarbons such as [2.1.0]bicyclopentanes (14) and spiropentanes (16) [14a,b]. The formation of the spiropentane 16 is particularly remarkable as it is the result of a homolytic hydrogen abstraction from a cyclopropane ring. Those processes are very rarely observed due to the relatively high C-H-bond energies of cyclopropanes (Sch. 8). 

The synthesis and properties of the highly symmetrical hydrocarbon phanes 2 and 6 have been reported in 197018 X-ray data of 619 indicate a molecular strain exceeding that of [2.2]paracyclophane-diene (7). The latter was estimated by Gantzel and Trueblood to be about 39 kcal/mole (163.0 kJ/mole)20). 

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