3-Spirocyclopropyl substitution

In a study of 3-spirocyclopropyl substituted 2-norbornyl p-nitrobenzoates in 70% aqueous acetone, Wilcox and Jesaitis found rate enhancements of about 10 and 10 for the exo- and ewiio-derivatives 41 and 42, respectively, over the corresponding non-spiro systems. The relative rates of the exo- and en o-3-spirocyclopropyl norbornyl derivatives... 

It is worth mentioning here that the spirocyclopropyl-substituted oxazoline-5-car-boxylates 2-172, as well as the corresponding thiazoline-4-carboxylates, can be transformed into cyclopropyl-substituted amino acids, which might act as potential enzyme inhibitors [93] and interesting building blocks for peptidomimetics [94]. 

Figure 10. Spirocyclopropyl substituted derivatives of 1,r-bicyclopropylidene (title compounds).

In a recent study in 80 % aqueous acetonea spirocyclopropyl substituted indan-l-yl p-nitrobenzoate (44) was observed to have unusually high reactivity indicating stabilization both by the cyclopropane and benzene rings. A Hammett pa study of substituent... 

The JV-benzyl aziridines 69, 92-95 which differ only in the nature of the norbomane bridge (CH2, spirocyclopropyl, isopropylidene, oxygen, substituted nitrogen) (Scheme 14), have been prepared and reacted with each of the corresponding benzonorbomadienes 36-40 from which they were derived. All 25 reactions were conducted to produce 14 of the possible 15 different... 

These authors also showed that the indolizidine skeleton can be prepared from cyclopropyl dipolarophiles (Scheme 1.16). The cycloaddition of alkyhdenecyclo-propanes 67 with various nitrones (e.g., 68) afforded the expected isoxazolidine adducts 69 and 70, commonly forming the C(5) substituted adducts 70 (97,105-108) predominantly but not exclusively (109-111). Thermally induced rearrangement of the spirocyclopropyl isoxazolidine adduct 70 afforded the piperidinones 71 (107,108). These authors propose reaction via initial N—O bond homolysis of 70 to diradical 72 followed by ring expansion through relief of the cyclopropyl ring strain forming the carbonyl of a second diradical intermediate 73, which cyclizes to afford the isolated piperidinone 71. 

The quaternary carbons of the tertiary cations 97 have chemical shifts of <5 l3C 69.2,61.1 and 58.8 for the Me, Ph and cyclopropyl substituted ions, respectively, which shows that progressively less charge is delocalized into the spirocyclopropyl ring going from methyl to phenyl to cyclopropyl. Consequently, the order of the stabilizing effects of the substituents on the cationic center is cyclopropyl > Ph > Me. 

---