Carbocyclic derivatives cyclopropane synthesis

Miscellaneous Iminium Catalyzed Transformations The enantioselective construction of three-membered hetero- or carbocyclic ring systems is an important objective for practitioners of chemical synthesis in academic and industrial settings. To date, important advances have been made in the iminium activation realm, which enable asymmetric entry to a-formyl cyclopropanes and epoxides. In terms of cyclopropane synthesis, a new class of iminium catalyst has been introduced, providing the enantioselective stepwise [2 + 1] union of sulfonium ylides and ot,p-unsaturated aldehydes.As shown in Scheme 11.6a, the zwitterionic hydro-indoline-derived catalyst (19) enables both iminium geometry control and directed electrostatic activation of sulfonium ylides in proximity to the incipient iminium reaction partner. This combination of geometric and stereoelectronic effects has been proposed as being essential for enantio- and diastereocontrol in forming two of the three cyclopropyl bonds. 

Reactions of cyclopropane derivatives activated by one type of functional group have been well understood and applied in organic synthesis for quite some time1). The far-reaching analogy between reactivity of olefins and cyclopropanes can be explained by the tc-type orbitals of strained three membered carbocycles and their interaction with the activating substituents 2,3>. 

Cyclopenten-l-ol, l,3-dimethyl-2-(7-methyl-3,7-tridecadien-ll-ynyl), , )-, 91-92, 279-280 2-Cyclopenten-1 -one, 3-methyl-2-(2-pentenyl)-, (Z)- (fasmone) synthesis, 29 2-Cyclopenten-l-ones syntheses by cyclizations from 1,4-dioxo compounds, 69, 79 from 5-nitro-l,3-diones, 81 Cyclophanes of porphyrins, 253 meta-Cyclophanes, 38, 338 pora-Cyciophanes = tricyclo[8.2.2.24,7]hexadeca-4,6,10,12,13,15-hexaenes synth., 38-39 Cyclopropane derivs. See Carbocycles, 3-membered... 

Abstract Transition metal-catalyzed cycloadditions of cyclopropanes have been well developed over the past several decades, leading to numerous new types of cycloadditions which are complementary to the traditional cycloadditions for the synthesis of carbocycles. Cycloadditions of vinylcyclopropanes (VCPs) and methylenecyclopropanes (MCPs) constitute two main aspects of this field. VCPs can act either as five-carbon synthons or three-carbon synthons, depending on whether the vinyl substituent is acting as an additional two-carbon synthon or not. As five-carbon synthons, VCPs are involved in [5-1-1], [5-1-2], [5-I-2-1-1], and [5+1+2-I-1] cycloadditions. As three-carbon synthons, VCPs are mainly involved in [3-1-2] and [3-1-2-t-l] cycloadditions. MCPs mostly act as three-carbon synthons and can have [3-1-2] cycloadditions with different jt systems. Other types of cycloadditions involving MCPs are also reviewed, such as [3-rl], [3+2+2], and [4+3+2] cycloadditions. CycloadditirMis of some other unusual cyclopropane derivatives are also introduced briefly. The cycloadditions of VCPs and MCPs have found applications in total synthesis and some representative molecules are tabulated as selected examples. 

---