## 2 Carbon-Carbon Forming Reactions
### Carbene Transfer Reaction  
Reactions where carbenes were transferred onto unsaturated substrates (alkenes, alkynes, arenes, amines, aldehydes etc. ), have provided a number of useful products [14; 15; 16; 17; 18; 19]. The mentioned carbenes can be generated in situ from diazo compounds by the application of transition metal-based catalysis [14]. The most widespread example of such reaction implemented at large scale is copper-catalysed cyclopropanation of substituted alkenes with alkyl diazoacetates. Therefore, many homogeneous as well as heterogeneous catalytic systems have been developed for this reaction [14; 15; 16; 17; 18; 19; 20]. In the case of Cu(I) complexes, bisoxazoline ligands [15; 16; 17; 18] and azabisoxazole ligands [19] were used, anchored on pearl-like polystyrene. For the immobilization of ligands either a copolymerization strategy (catalysts **3** and **4**) or post-modification strategy (catalysts **5**-**7**) was utilized. The catalysts were generated in situ by the coordination of copper(II) triflate and consequent reduction with phenylhydrazine (Scheme 3) [15; 16; 17; 18; 19; 20]. Catalyst **3** was prepared by copolymerization of corresponding bisoxazoline-bearing styrene (4%) with styrene (42%) and DVB (54%), which gave a highly cross-linked polymer having a compact structure (<5 m\({}^{2}\) g\({}^{-1}\)) [15; 16]. Cyclopropanation catalysed by **3** was tested on the reaction of ethyl diazoacetate with styrene (60%, _trans/cis_: 67/33, 93% enantioselective excess (eee)) (Scheme 3); with 1,1-diphenyllethene (97%, 98% ee) and with 2-methylpropene (92%, 97% ee) [16]. Catalyst **3** was fivefold reused in the reaction of styrene with ethyl diazoacetate without any significant decrease in yield and enantioselectivity. Modification in the preparation of catalyst **3** by performing of copolymerization in different ratios of bisoxazoline-bearing styrene (6%) with styrene (92%) and DVB (2%) did not affect either the isolated yield (67%), or the diastereoselectivity (67/33) and enantioselectivity of cyclopropanation (92% ee) [16]. Likewise, a change of strategy of preparation for catalyst **3** (post-modification of Merrifield resin(tm)) did not lead to any significant impact on the catalyst(s) efficiency [16]. Poor enantioselectivity found for catalysts **4** (36%, _trans/cis_: 37/63, 78% ee) [17] and **5** (18%, _trans/cis_: 66/34, 26% ee) [17], and **6** (60%, _trans/cis_: 64/36, 65% ee) [18],was explained by lower binding affinity towards copper, caused by the change of geometry of the ligand as a consequence of the replacement of the _gem_-dimethyl substitution box-bridge with sterically large groups [19]. A notable improvement in binding affinity towards copper was achieved by using of azabisoxazol ligament; moreover, it also led to an increase of the catalyst **7**'s efficiency (94%, _trans/cis_: 74/26, 99% ee) [19]. An improvement in enantioselectivity (79% ee, _cis_)--explained by the effect of the \"chiral-cavity\" of the rigid polymer--was later achieved for the highly-crosslinked catalyst **4**, which was prepared according to the copolymerization strategy [20]. Even in this case, the influence of post-modification strategy or copolymerization strategy was not significant. On the other hand, testing confirmed that the Merrifield resin(tm) used in catalyst **7** was a much better support than TentaGel(tm) (35%, _trans/cis_: 64/34, 47% ee) [19]. The next reusable catalyst **8** was prepared by coordination of [Cu(MeCN)4][PF6] on tris(triazolyl) methane anchored on commercial Merrifield resin(tm) (Scheme 4) [20]. Reactions of catalyst **8** with ethyl diazoacetate led to formation of carbene (:CHCO\({}_{2}\)Et), which was used for six reactions with following substrates: cyclohexane (C-H insertion), tetrahydrofuran (THF) (C-H insertion), ethanol (O-H insertion), aniline (N-H insertion), phenylacetylene (cyclopropation), and benzene (cyclopropation/ring expansion).