Spiro-cyclopropyl groups

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... 

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. 

Bis(trimethylsiloxy)spiro[2.3]hex-4-ene, which is structurally related to i,2-bis(trimethyl-siloxyjcyclobutene, underwent high-pressure catalytic hydrogenation over a nickel catalyst to give ra-4,5-bis(trimethylsiloxy)spiro[2.3]hexane (32) in 78% yield.41 It is noteworthy that the cyclopropyl group was not cleaved under the reaction conditions. 

Previously discussed spiro[2.5]oct-4-yl cation 34148 is also a cyclopropylmethyl cation with substantial positive-charge delocalization into the cyclopropyl group. Other representative cyclopropylmethyl cations that have been prepared in the... 

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... 

With simple secondary spirocyclopropylcarbinyl systems the cyclopropyl group, owing to its favorable bisected geometry for orbital overlap, generally produces a rate acceleration of about 10 over corresponding 2,2-dimethylcycloalkyl systems The relative rates for the secondary spiro systems shown below " " are for typical... 

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). 

The de Meijere group [63] prepared interesting spiro-compounds containing a cyclopropyl moiety using a combination of a Heck and a Diels-Alder reaction, with bicyclopropylidene 6/1-115 as the starting material. The transformation can be performed as a three-component process. Thus, reaction of 6/1-115, iodobenzene and acrylate gave 6/1-116 in excellent yield. With vinyliodide, the tricyclic compound 6/1-117 was obtained (Scheme 6/1.31). Several other examples were also described. 

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