Indicated spirocycles

In two separate reactions, a new carbon-carbon double bond was created by the insertion of a heteroallene into the Al-C-Al bonds of a spirocyclic dimethylaluminum bis(iminophosphorano)methandiide compound (Figure 2(b)).47 In both compounds, the C-C bond is shorter than a single bond but longer than a typical double bond, indicating delocalization within the interesting bicyclic ring systems. 

The probable course of another general reaction is indicated in the example of the spirocyclic ketal (761) with hydroxylamine. The isolated dioxime is subsequently cyclized by treatment with acid (54BSF1139). 

The occurrence of a similar reaction has recently been indicated by studies carried out in this laboratory (7). If p-hydroxybenzyl alcohol (XXXVI) was oxidized with sodium bismuthate, the spirocyclic epoxy-cyclohexadienone (XXXVII) was obtained. The epoxide ring of this compound was hydrolyzed almost instantaneously by 2N aqueous hydrochloric acid and in a few hours by 10% aqueous acetic acid. However, the expected glycol (XXXVIII) could not be isolated since it decomposed immediately into equimolar amounts of hydroquinone and formaldehyde. (Attempts are now being made to prepare compounds analogous to XXXVIII but containing, in addition to the HOCH2 group, a carbon sub-... 

The intramolecular nitrogen-trapping protocol used by Banwell has also been successfully exploited in the assembly of spirocyclic frameworks relating to the aromatic erythrina alkaloids.24 However, when it was applied to the synthesis of nonaromatic spirocycles, as found in histrionicotoxin, the flexible alkyl tether proved to be problematic.25 In this study, gem-dichlorocyclopropane substrate 37 was initially subjected to silver(I) salts under a variety of conditions only to provide solvolysis and elimination products without any indication of trapping by the pendent... 

For the spirocyclic tin complexes 113a and 109b, the Sn—S bond lengths are much closer. They are two shorter ones, averaging 2.458 and 2.521 A, and two longer ones, averaging 2.455 and 2.516 A, respectively324. This small difference is indicative of a residual TBP character that was expressed by the ca 94 and 97% displacement toward RP. 

The AGe values in the spirocyclic derivatives (Table 39) are smaller than those in regular germocanes. Thus the TBP coordination polyhedra of the Ge atoms in the former are less distorted. The N —> Gc distances in spirocyclic germocanes are also smaller, which indicate a stronger coordination in these compounds. 

The latter example (reaction 36) already indicates that the Yang cydization can also be used to synthesize four-membered heterocycles. After light absorption, the a,(3-unsaturated carbonyl compound 84 undergoes intramolecular hydrogen abstraction at the a-position of the carbonyl moiety (reaction 37), leading to the 1,4-biradical intermediate XXX [87]. A radical combination then efficiently yields the spirocyclic P-lactam derivative 85, and only one stereoisomer is formed in this case. In this transformation, the a,P-unsaturated carbonyl function can be considered as being vinylogous to a simple ketone. 

Some analogous rathenium- and osmium-bismuth clusters have been found. Examples include Bi2M3(CO)9 and H3BiM3(CO)9 (M = Ru, Os). The stmctures of the hydride compounds have both been determined and they are isostractural with the iron complexes as is Bi2Ru3(CO)9 withBi2Fe3(CO)9. The structure 0fBi2Os3(CO)9, on the other hand, has not been determined and its IR spectrum indicates that it probably has a different structure. A spirocyclic cluster [Ru2(CO)8(/X4-Bi)Ru3(CO)io(/x-Ft)] (39) has been reported. 

Studies performed by Carriedo et al. indicated that the spirocyclic phosphazene polymer 37 can adopt a helical conformation in solution.146 Yashima et al. subsequently investigated the chiroptical response of 38 (Chart 7) upon complexation with (/v)-a-phenyl-ethylamine in DMSO.147 The resulting optical rotation and its response to changes in temperature... 

Figure 2.11 The mechanism of fullerene formation by spirocyclization. Indicated to the left and in the middle possible reaction schemes for the formation of six-membered (top) and five-membered rings (bottom).

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