# Approaches to the Functionalization of Organosilicon Dendrones Based on Limonene
## 3 Results and Discussion
### Opening of the Oxinne Ring in Limonene-Based Carbosilane and Carbosilane-Siloxane Dendrons  
From the perspective of applied chemistry, the synthesis of dendrons with an oxirane ring at the focal point is of interest, primarily due to the possibility of its opening on treatment with both nucleophiles and electrophiles. The simplicity of oxirane ring opening along with the possibility of further incorporation of a wide range of functional groups offer innumerable options for further chemical transformations of the dendrons obtained.  
Thus, in this work, we have shown the possibility of epoxide ring opening in dendrons with various nucleophiles that are of interest for further applications, including azide, thiolate, carboxylate, and hydride anions. The carbosilane-epoxidized dendron Lim-G\({}_{1}\)Bu\({}^{4}\) was chosen as the model compound for these purposes. It was chosen for three reasons: first, because of the simpler NMR spectroscopic analysis of the products obtained upon oxirane ring opening; second, because the possible splitting of the siloxane bond in carbosilane-siloxane dendrons was prevented; and third, because it is CDs that are required in the subsequent synthesis of JDs.  
As regards further functionalization, the incorporation of the azide function is of great interest because it can be used for azide-alkyne cycloaddition and can be reduced to an amino group. The opening of the epoxide ring with sodium azide was performed under standard conditions by refluxing in methanol with sodium azide (Scheme 3, on the right) [51]. The progress of the reaction was monitored by \({}^{1}\)H NMR spectroscopy through the disappearance of the characteristic signals of oxirane protons \(\delta\) = 3.01 and 2.96 ppm. The yield of the product was 88%. It was shown that during the epoxidation of limonene dendrons, a mixture of regioisomers is formed in a ratio of 1:1. Using APT spectra, two signals of multiple carbon substitution (71.11 ppm and 63.19 ppm) and two signals of non-multiple carbon substitution (72.17 ppm and 66.72 ppm) were shown (Figure 3). The HSQC spectrum has cross-peaks, characterizing the C-H correlations for the azide group and for the hydroxyl group (Figure 4). According to the mechanism of this reaction, functional substituents (hydroxyl and azide groups) always take an axial position in the cyclohexane ring.  
**Scheme 3. Cleavage of oxirane cycle of CDs based on epoxylimonene by different nucleophiles.**Figure 3: APT NMR spectrum of \(LimN_{3}\)-\(G_{1}Bu^{4}\).  
The ethynyl group is yet another important function involved in the azide-alkyne cycloaddition reaction. Therefore, we made an attempt to perform oxirane ring opening with propagylic acid (Scheme 3, on bottom). The reaction was performed without a solvent with heating at 70 \({}^{\circ}\)C for 6 h until complete conversion. After isolation, the product yield was 90%.  
We also studied the possibility of reducing the epoxy ring to an alcohol group. Reactions of this kind result in a secondary alcohol upon treatment with reducing agents such as metallic sodium or lithium aluminum hydride (Scheme 3, on the left).  
Refluxing of the corresponding epoxide with lithium aluminum hydride was shown to result in complete opening of the oxirane ring. The product yield after isolation was 86%.  
An attempt to perform the oxirane ring opening with thiolate (Scheme 3, on top) failed to yield a noticeable conversion according to \({}^{1}\)H NMR spectra; hence, it is of no preparative value.