Spiro-cyclopropyl

Spiro-pyrazoline derivatives (18) are obtained smoothly from 16-methy-lene-17-ketones (17). ° The sole products formed from (18) by pyrolysis or cleavage in the presence of boron trifluoride etherate, are the 16-spiro-cyclopropyl steroids (19). ... 

Initial thermal sigmatropic 1,5-carbon shifts are believed to account for the product formation from spiro[2.4]hepta-4,6-diene (l) 200 and spiro[cyclopropyl-l, 2 -2 //-indene] (6),201 obtained by photodecarbonylation of dione 5. In the first case, a 1,5-hydrogen shift and an electrocyclic ring opening completes the formation of 3,4-dimethylenecyclopent-l-ene (4),200 and in the second case, the initially formed benzoannulated bicyclo[3.2.0]hepta-l,3-diene 7 dimerizes to 8 as mixture of two stereoisomers.201... 

In consideration of these results" de Meijere concluded" the cyclopropyl group has an inductive electron-attracting effect in this case and destabilizes the intermediate carbenium ion . However, the destabilization referred to is for spiro cyclopropyl relative to a tert-butyl... 

These reactions demonstrate not only the strong 7r-donor ability of cyclopropyl but also the conformational dependence of this effect Thus the partial rate factors for nitration of 117 and 119 as compared to the models 118 and 120 reveal that the spiro-cyclopropyl in 117, which is fixed in the bisected conformation, is considerably more... 

In more recent work, Leandri and coworkers have solvolysed a series of methylene dialkyl and methylene spiro cyclopropyl bromides as a method for preparing a-allenic tertiary alcohols. An example is shown below in the reaction of 1. Robertson and... 

Several secondary dispirocyclopropylcarbinyl systems have been studied by Krapcho and coworkers giving the relative rates in 80 % aqueous acetone at 50°C shown. Thus, in both the spiro[2,4] and spiro[2,5] systems the second spiro cyclopropyl group causes an... 

The presence of an a-methylene group permits the enoli-zation of the hit molecule, this tautomery is blocked through the insertion of a spiro cyclopropyl ring (Figure 19.13). Result of a formal oxidation yields the secondary alcohol. Double bond possibilities are a-methylene (X = CH2), the diketone (X = O) and the corresponding ketoxime (X = N-OH). 

Gem-dimethyl and spiro-cyclopropyl are useful to render a carbon atom quaternary and therefore resistant to metabolic attacks. 

Very recently the synthesis of derivatives which incorporated a spiro-cyclopropyl group at N-1 by bridging to C-2 was reported [53]. The fused spiro-cyclopropane ring was obtained through an intramolecular addition of Grignard reagent, as shown in Fig. 20. 

An important achievement in this field has been realized during the total syntheses of the spiropyrrolidine-oxindole alkaloid (zt)-strychnofoline 107 (Scheme 41.23)." " Isolated from the leaves of Strychnos usambarensis, strych-nofoline displays antimitotic activities against cultures of mouse melanoma and Ehrlich tumor cells. Carreira and coworkers developed a methodology in which the key [3+2] annulation was performed by the treatment of spiro-cyclopropyl-3,3 -oxindole 102 with an iV-alkyl imine 103... 

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