Heterocycles from dienes

Without additional reagents B-Heterocyclics from dienes... 

Azadienes, synthesis of heterocycles from (review), 57, I I-Aza-1,3-dienes cheletropic addition to... 

Scheme 15. Synthesis of Heterocycles from 1,6-Dienes, Enynes, and Diynes via (a) Cycloisomerization, (b) Tandem Addition—Cyclization, and (c) Cycloaddition...

Formation of fused heterocycles from acetylenic or allenic sulfones and pyrroles or furans as dienes 01T5263. 

Metathetic ring closure. Five-, six-, and seven-membered carbocycles as well as N and O heterocycles are constructed from dienes in the presence of a Ru-carbene complex. For unhindered amines, prior protonation is necessary. Fused bicyclic structures are accessible from dienynes. ... 

This bond order deviation from an ideal transition state structure to an example of cyclopropene added to a benzo-fused heterocycle may now be applied. Before we exEunine bond order deviation from an ideal transition state, we can take a look at the sums of rings bond order in the transition state structures. To simplify this picture, we will focus only on exo transition state structures between cyclopropene and benzo[c]heterocycles. Previously, we mentioned that the Diels-Alder reaction with benzo[c]heterocycles as dienes is a HOMO controlled diene reaction, therefore, an electron rich (higher sum of bond order) transition state structure should be energetically preferred. If this is the case, the order of reactivity should be benzo[c]furan, benzo[c]thiophene, and then benzo[c]pyrrole, which is exactly the same as determined on the basis FMO energy change (Table 23). 

Synthesis of partially fluorinated heterocycles from 4,4-bis(trifluoro-methyl)-substituted hetero-1,3-dienes via C—F bond activation and their application as trifluoromethyl-substituted building blocks 06H (69)569. 

S.2.2.7. Fused Heterocycles from Cyclic Dipolarophiles. Furan provides a useful example of a diene acting instead as a dipolarophile. As will be discussed in Chapter 6, this molecule has the lowest aromaticity of the 5-membered heterocycles. It is also useful as a diene in Diels-Alder cycloadditions, but here we will observe that one double bond can react with a 1,3-dipole (Scheme 5.34). 

A reaction sequence involving double Heck reactions/C-H activations was adopted by Hu and coworkers [6] to synthesize tri- and tetracyclic [7] fused N-heterocycles 13 and 14 from dienes 10 and 11, respectively (Scheme 3.2). 

P-Napthalenesulfonic acid N-Condensed heterocyclics from 5-alkoxyhydantoins and 1,3-dienes Stereospecific ring closure... 

Buiger K, Helmreich B, Hennig L, Spengler J, Albericio F, Fuchs A (2007) Partially fluori-nated heterocycles from 4,4-bis(trifluoromethyl)-hetero-l, 3-dienes via C-F bond activation -synthesis of 2-fluoro-3-(trifluoromethyl)furans. Monatsh Chem 138 227-236... 

In this chapter we focus on the selective synthesis of aromatic hydrocarbons and heterocycles from unsaturated molecules by using zirconocenes and titanocenes via transmetallation to other metals, such as Cu, Ni, and Li. Although there are several examples of aromatic ring formations directly from metallacycles, we emphasize the cooperative effects in particular, transmetallation from group 4 metals to the other metal species. The coupling reaction of a Cp ligand with the diene moiety in a... 

Sugiyama, H., Yokokawa, E., and Shioiri, T. (2000) Asymmetric total synthesis of (—)-mycothiazole. Org. Lett., 2, 2149-2152. Rodriguez-Conesa, S., Candal, P., Jimenez, C., and Rodriguez, J. (2001) An enyne metathesis approach to the synthesis of the 1,3-diene system of mycothiazole. Tetrahedron Lett., 42, 6699-6702. Sugiyama, H Yokokawa, F., and Shioiri, T. (2003) Total synthesis of mycothiazole, a polyketide heterocycle from marine sponges. Tetrahedron, 59, 6579-6593. 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Tamariz and coworkers [42] have described a versatile, efficient methodology for preparing N-substituted-4,5-dimethylene-2-oxazolidinones 42 (Figure 2.5) from a-diketones and isocyanates and have also studied their reactivity in Diels-Alder reactions. This is a method for synthesizing polycyclic heterocyclic compounds. Some of the reactions of diene 42 are summarized in Scheme 2.18. The nitrogen atom seems to control the regiochemistry of the reaction. 

Indole-2,3-quinodimethanes [44] 44 are bicyclic outer-ring dienes that are widely used to prepare a variety of heterocyclic polycyclic compounds. These dienes, generated by extrusion of CO2 from lactones, are then trapped by dienophiles. Some examples of Diels Alder reactions of the dienes 44 are reported in Scheme 2.19. 

Silylthioaldehydes 103, reactive dienophiles formed in situ from acetals according to a general method, are directly trapped with dienes to afford sulfur-containing heterocyclic compounds in good yield (Equation 2.29). Silylthioaldehydes are quite reactive in comparison with the aliphatic ones [102] which are rather inert in the cycloaddition reactions. 

Chiral heterocyclic compounds containing vicinal oxygen and nitrogen atoms were achieved by an asymmetric Diels-Alder reaction [111] of chiral acylnitroso dienophiles 111. The latter were prepared in situ from alcohols 110, both antipodes of which are available from camphor, and trapped with dienes (Scheme 2.46). Both the yield (65-94 %i) and diastereoisomeric excess (91-96%) were high. 

---