Spiro alkan

The simplest spiro alkane is spiro[2.2]pentane, a molecular model of which illustrates an interesting structural feature of spiro compounds. The two rings lie at right angles to each other. 

Diazirines, which are structural isomers of diazoalkanes, similarly extrude nitrogen to give carbenes. Thus, the adamantylidene derivative (118) gives the spiro-alkane (119) on heating in cyclohexene. 

The lUPAC names of spiro alkanes take the form spiro[number.number]alkane. The alkane suffix is simply the name of the unbranched alkane having the same number of carbons as those in the two rings. The numbers inside the brackets are, in ascending order, the number... 

A further example of the importance of this type of stereoelectronic effect is seen in the reactions of /-butoxy radicals with spiro[2,n]alkanes (22) where it is found that hydrogens from the position a- to the cyclopropyl ring arc specifically abstracted. This can be attributed to the favorable overlap of the breaking C-H bond with the cyclopropyl cr bonds.120131 No such specificity is seen with bicyclo[n, 1,0]alkanes (23) where geometric constraints prevent overlap. 

A particularly interesting case was the oxidative spiro dimerization of a,CO-bis (tocopheryl)alkanes (36), which basically present two a-tocopherol units linked at C-5a by an alkyl bridge.59 The reaction of other a,0)-bis(hydroxyphenyl)-alkanes, such as 37—40, proceeded similarly (Fig. 6.30). 

FIGURE 6.30 a,cu-Bis(tocopheryl)alkanes (36) and other a, >-bis(hydroxyphenyl)-alkanes (37-40) as starting materials for the spiro oligomerization/spiro polymerization reaction. 

FIGURE 6.31 Spiro polymerization of a, spiro polymers 41 carrying spiro dimer units linked by alkyl chains. Reduction of 41 converts the spiro dimer units into ethano-dimer units, resulting in polytocopherols 42. 

I. 1-anthryl-l -naphthyl alkanes. II. Nicotinamide-adenine-dinucleotide (reduced) NADH. IFF Oligomers of poly-L-proline with a-naphthyl group as energy donor and dansyl group as energy acceptor. III. p-methoxy benzene and flourene chromophere in norbornadiene-spirocyio-propane frame. V and VI. Anthrone and naphthalene chromphore in spiro-compounds. 

Prior knowledge has shown the value of introducing cyclopropane systems into macromolecules. A number of isolated studies have been carried out on the polymerization of such structures (10, 14, 28), principally on cyclopropane (28) and isopropylcyclopropane. Attention was directed toward three types of structures—i.e., the 1,1-dichlorocyclopro-panes, the bicyclo[n.l.0]alkanes, and the spiro [2.n] alkanes. In each case, the effects involved appeared highly complex the polymers formed have not yet all been characterized, and it is thought that a comparison with the model structures expected from rupture of one or the other of the cyclopropane bonds may be of value. 

First, following the results of the 1,6-dioxa-spiro[2.5]octane rearrangement (5,19), continuous gas phase conditions were applied in a fixed bed reactor and secondly under liquid phase conditions in a slurry reactor. The catalytic experiments carried out showed that two main reactions took place rearrangement of 18 to the aldehyde 19 and a oxidative decarbonylation reaction to the olefine 1,3,3,4-tetramethyl-cyclohex-l-ene 20, which is assumed to be caused by a formaldehyde elimination reaction. Also observed was a deoxygenation reaction to the alkane 1,1,2,5-tetra-methylcyclohexane 21 (Eq. 15.2.7), explained by elimination of CO. There are several other side-products such as 2,2,3,6-tetramethylcyclohex-l-enyl-methanol, ringcontracting compounds and double bond isomers of dimethyl-isopropylene-cyclopentene. 

Dioxa-spiro 4.n]alkan 6-Oxo-E14a/1, 203 (Dion + Glykol)... 

Spiro ring systems are named as spiro[x.y]aIkanes where the parent alkane corresponds to the total number of carbons in both rings, and x and y refer to the number of carbons that join the shared carbon (the spiro carbon), written in order of increasing size. When substituents are present, the rings are numbered beginning with a carbon adjacent to the spiro carbon in the smaller ring. 

Spiro[2.5]octadienyl radical (146), the radical analog of the phenonium ion (105), is a very short-lived species but was detected by its visible absorption and fluorescence on generation by radical abstraction from 147 prior to facile ring-opening to 148 (equation 29). There appeared to be a modest (two-fold) acceleration compared to 1,3- or 1,4-cyclohexadiene in the rate of abstraction from 147, and this was attributed to stabilization by a favorable interaction between cyclopropyl and the adjacent semioccupied orbital in 146. Kinetic acceleration was also proposed to occur in hydrogen atom abstraction from spiro[2.n]alkanes (149). ... 

The solvolysis of spiro[2.n]alkan-4-ol derivatives leads to ring enlargement products. In particular, solvolysis of spiro[2.3]hexyl-4-(3, 5 -dinitrobenzoates) (ODNB) (237) in 80% aqueous acetone gives a mixture of five-membered ring compounds derived from C3 - C5 ring expansion (equation 156) . 

The anodic oxidation of polyalkyl substituted cyclopropanes and spiro[2.n]alkanes gave mono- and dimethoxy products which resulted from the cleavage of the most highly substituted C-C bond, in contrast to the results obtained by acid-catalyzed methanolysis of alkyl-substituted cyclopropane by the same authors. Those results suggest that a direct (7-electron transfer from the most strained a bond of cyclopropane to the anode may be the initiation step. 

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