Cyclization double reaction

A stereoselective one-pot synthesis of furo[3,2- ]pyran, 80, has been reported. The key step in the synthesis includes a double cyclization reaction along with a rearrangement (Scheme 16) <1998TL3605>. 

Also in 2010, the Jacobsen group reported the combined use of hydrochloric acid and thiourea catalysts for the highly enantioselective cationic double cyclization reaction initiating from an A-acyliminium ion (Fig. 23) [78]. The catalyst optimization research led to the identification of a pyrenyl-substituted thiourea structure, which seems to indicate the importance of cationic-Ti interaction during this reaction. 

Reactions. In addition to the usual reactions of primary hydroxyl groups and of double bonds, i j -butenediol undergoes a number of cyclization reactions. 

Reactions involving quinoline hydrazide derivatives have been noted in the pyridazino-[4,3-c]- (64MI21500), -[4,5-f ]- (31M(58)238) and -[4,5-c]-quinoline (71CB3341) series, whilst the double cyclization of (358) to the pyridazino[4,5-f ]quinoline (359) (80CPB3457) and related cyclizations in the same series (80H(14)267) are of a basically similar type. A lone cyclization of this type from cinnoline intermediates involves the o-acetonylcarboxamide type formation of the pyridine ring to give the pyrido[3,4-c]cinnoline (360) (76JCS(Pl)592). 

The addition, therefore, follows Markovnikov s rule. Primary alcohols give better results than secondary, and tertiary alcohols are very inactive. This is a convenient method for the preparation of tertiary ethers by the use of a suitable alkene such as Me2C=CH2. Alcohols add intramolecularly to alkenes to generate cyclic ethers, often bearing a hydroxyl unit as well. This addition can be promoted by a palladium catalyst, with migration of the double bond in the final product. Rhenium compounds also facilitate this cyclization reaction to form functionalized tetrahydrofurans. 

Dendrimers 5-8 were obtained by taking advantage of the versatile regiose-lective reaction developed in the group of Diederich [24], which led to macro-cyclic bis-adducts of Cgg by a cyclization reaction at the C sphere with bis-mal-onate derivatives in a double Bingel cyclopropanation [25]. Reaction of the dendritic malonates with Cgg, I2, and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene at room temperature afforded the corresponding cyclization products 5-8 (Fig. 2). The relative position of the two cyclopropane rings in 5-8 on the Cgo core was determined based on the molecular symmetry deduced from the and NMR spectra (Cs) as well as on their UV/Vis spectra. It is well estabhshed... 

Anionic domino processes are the most often encountered domino reactions in the chemical literature. The well-known Robinson annulation, double Michael reaction, Pictet-Spengler cyclization, reductive amination, etc., all fall into this category. The primary step in this process is the attack of either an anion (e. g., a carban-ion, an enolate, or an alkoxide) or a pseudo anion as an uncharged nucleophile (e. g., an amine, or an alcohol) onto an electrophilic center. A bond formation takes place with the creation of a new real or pseudo-anionic functionality, which can undergo further transformations. The sequence can then be terminated either by the addition of a proton or by the elimination of an X group. 

The formation of the indole moiety has found immense attention, since it exists in many bioactive compounds such as the indole alkaloids [302]. Whilst the Fischer indole synthesis remains the most important procedure, during the past few years several transition metal-catalyzed syntheses have been developed. Recently, a Cu11-catalyzed cyclization of anilines containing an ortho-alkynyl group was published by Hiroya and coworkers [303], which allows a double cyclization in domino fashion to provide annulated indoles. Thus, reaction of 6/4-92 in the presence of... 

Reaction of phenyl vinyl ketone with cyclopentanone under thermal conditions resulted in a diastereomeric mixture of 1,5,9-triketones 374 via a double Michael reaction. Treatment of this mixture with ammonium formate in polyethyleneglycol-200 under microwave irradiation conditions led to the very fast and efficient formation of a 2 1 diastereomeric mixture of cyclopental flquinolizidines 375 and 376 <2002T2189>. When this reductive amination-cyclization procedure was carried out starting from the purified /ra r-isomer of 374, the result was identical to that obtained from the cis-trans mixture, showing the operation of thermodynamic control (Scheme 86). 

A ,A"-/i/. s,(dimcthylaminomcthylenc)thiourea (prepared by double condensation of AAY-dimethylformamide dimethyl acetal with thiourea) has been reacted with a-haloketones or acrylic dienophiles to give thiazolic and thiazinic diazadienes, respectively. These undergo cyclization reactions to yield imidazo[2,1-/ ][1,3] thiazoles, 5H-1,3-thiazolo[3,2-a]pyrimidines, 72/-imidazo[2,1 -/ ][ 1,3]thiazines and 2//,6//-pyrimido[2,l -/)][1,3]thiazines without any regioisomeric ambiguity (Scheme 61).144,145... 

Unlike nickel Catalysts, palladium complexes do not catalyze the homo-cyclization reaction to give CDT or COD. The difference seems to be due to a different degree of hydride shift and atomic volume. With palladium catalysts, the hydride shift is easier, and hence linear oligomers are formed. The characteristic reaction catalyzed by palladium is the cocyclization of two moles of butadiene with one-hetero atom double bonds such as C=N and C=0 bonds to give six-membered rings with two vinyl groups (19) ... 

Oxygen-free reactions of psoralens, when in close proximity to the target, proceed via the first excited states in which the 3,4-and the 4, 5 7r-bonds of the pyrone and furan moieties, respectively, can undergo C4-cyclization reactions with, e.g., unsaturated bonds of lipids, or the C5=C6 double bonds of thymine in DNA. In reactions with DNA the psoralen is believed to intercalate with DNA in the dark. Subsequent irradiation at 400 nm usually leads to furan-side 4, 5 -monoadduct formation, whereas irradiation at 350 nm increases the formation of crosslinks in which the furan and pyrone rings form C4 cycloadducts to thymines on opposite strands [95], Subsequent irradiation of the 4, 5 -monoadducts at 350 nm leads to formation of crosslinks and conversion into pyrone-side 3,4-monoadducts. Shorter wave-... 

Ma et al. described the palladium(0)-eatalyzed three-component tandem double-addition-cyclization reaction of 2-(2,3-allenyl)malonate 218, Phi, and A-Ts-imine 219 for the stereoselective synthesis of 2,5-m-pyrrolidine 220... 

Alkynes are interesting radical acceptors for cyclization reactions because the products contain double bonds that can be subjected to further transformations. In the case of terminal alkynes, the desired products can be obtained in high yields as single isomers. With non-terminal alkynes as acceptors, the alkene products are generated as mixtures of ( )- and (Z)-isomers in high yields but with low selectivity [36],... 

Mechanistic insight into this process was obtained by administration of labeled trideca- or undeca-3,6,9-trienoic acid instead of the natural C12 precursor (Figure 2). In this case, the artificial 2H metabolites can be analyzed by mass spectrometry without interference from the plants own 1H metabolites, since a homo- or norectocarpene is formed. The sequence of the oxidative decarboxylation/cyclization reaction proceeds without loss of 2H atoms from the double bonds but with loss of a single 2H atom from certain methylene groups of the precursor acids (Figure 3). If C(l) and a 2H atom from C(5) of the labeled precursor is lost, finavarrene is the product of the reaction channel. If the methylene group... 

The examples illustrated in the almost 100 schemes in this chapter demonstrate how versatile donor-substituted allenes can be in synthetic processes. The major applications concern addition reactions and cycloadditions to the allenic double bonds, which furnish products with valuable functional groups. Of particular interest are metalations - usually at C-l of the allene unit - followed by reactions with electrophiles that deliver compounds which can often be used for cyclization reactions. A variety of highly substituted and functionalized heterocycles arises from these flexible methods, which cannot be obtained by other reactions. Many of these transformations proceed with good regioselectivity and excellent stereoselection. 

---