Tandem cyclization-capture

RXN64 Tandem Cyclization-Capture Process of Enynes... 

Grigg developed several palladium-catalyzed tandem cyclization-anion capture processes, and these include organoboron anion transfer agents [112, 164, 206]. Two examples of this methodology are shown. 

Z-tamoxifen 403 tandem cyclization 290, 295 tandem Heck reaction-anion capture 253-4 tandem Heck reaction-phenoxide capture 253 tandem Heck reactions 251, 252-4 tandem intramolecular Heck-intermolecular Stille cross-coupling 255 taxol 140, 143,243,245 ( )-tazettine 146,234 telomerization 352 telomerization products 343, 345 template effect 140 teraconic anhydride 468 terminal acetylenes, synthesis of 216-20 terminal alkynes 6, 213 terminal 2,2-diorgano-l-aIkcnylboronates 51 terminal diynes 207 ternary complex 444 ternary coupling 177... 

Queguiner made great use of Suzuki methodology to prepare heterobiaryls for use in carboline synthesis [169]. This chemistry is discussed in Chapter 4. As explored in more detail in Section 3.5, Grigg developed several Pd-catalyzed tandem cyclization-anion capture processes, and these include organoboron anion transfer agents [109, 170, 171], Two examples of this methodology are shown. 

Grigg and coworkers have used 2-tributylstannylfuran to terminate a variety of interesting tandem cyclization-anion capture reactions. In one example, aryl iodide 105 reacts via a 5-exo-trig process to provide dihydroindolone 106 [105-107]. 

Bicyclization-anion capture Strained bicyclic systems can be prepared by a tandem cyclization-anion capture process using a Pd catalyst in combination with sodium formate, tricthylaminc, or K2C02... 

RXN12 Tandem Cyclization-Anion-Capture Process ... 

RXN13 Tandem Cyclization-Anion Capture (-Carbonylation) Process of Yne-Vinyl and ... 

RXN12 Tandem Cyclization-Anion-Capture Process of Ene-Vinyl, Ene-Aryl and Ene-Alkyl Halides... 

Diaz, P., Gendre, R, Stella, L. and Charpentier, B. (1998) New synthetic retinoids obtained by palladium-catalyzed tandem cyclization-hydride capture process. Tetrahedron, 54, 4579-90. 

The radical produced from the oxidative decarboxylation may also be trapped intramolecularly to form five- and six-membered rings (Scheme 17). The Kolbe protocol avoids the use of the toxic organ-otin reagents that are commonly used in the formation of radicals. Moreover, when alkyltin hydride reagents are used, a C—H bond is formed. The Kolbe reaction protocol, on the other hand, allows the radical formed after cyclization to be captured by a different radical in a coelectrolysis experiment, rather than being reduced. This tandem sequence of events has been exploited in the construction of prostaglandin precursor (70) [37-41]. Here, the cyclized... 

Weng, H., Scarlata, C., and Roth, H.D. (1996) Electron transfer photochemistry of geraniol and (E, E)-farnesol. A novel tandem , 1,5-cyclization, intramolecular capture. Journal of the American Chemical Society, 118, 10947-10953. 

To control the equilibrium position of the rearrangement, Overman and others introduced a nucleophilic hydroxyl group at the C2 position to capture the rearranged iminium ion2 (Scheme 1.6b). Although the levels of diastereoselecti-vity for the formation of pyrrolidines 6a and 6b are low, the tandem cationic aza-Cope-Mannich cyclization provides a variety of substituted 3-acylpyrrolidines in high yields under mild reaction conditions. The first step in the reaction is the... 

Nuss and co-workers have demonstrated that a tandem Heck cyclization-anion capture process can access substructures related to vitamin D [58] and the neocarzinostatin chromophore (162) (Scheme 6-28) [59]. In a one-pot procedure, diiodide 159 was converted into dienediyne 160 in low yield. In this reaction, the alkyne undergoes Heck... 

Deoxygenative cyclization to form 5- and 6-membered rings from (O-halo aldehydes by irradiation (350 nm) and its mixture with BUjSnH and PhjP is a useful method. The cycloalkoxy radicals are captured in situ by triphenylphosphine which eliminate PhjP=0 and the carbon radicals are supplied with hydrogen from the tin hydride. Tandem radical cyclization processes are possible. 

For previous reports of tandem Heck reaction-anionic capture sequences, see (a) Grigg, R., Sridharan, V. and Xu, L.-H. (1995) Palladium-catalyzed cyclization-amination of allenes - effect of base on regioselectivity of formation of allylic amines. J. Chem. Soc., Chem. Commun., 1903 and references cited therein (b) Ma, S. and Negishi, E. (1995) Palladium-catalyzed cyclization of general route to common, medium, and large ring compounds via cyclic carbopaUadation. J. Am. Chem. Soc., 117, 6345-7 and references cited therein. 

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