Dienylic cyclic carbonates

Extension of this reaction to the dienylic cyclic carbonate 558, easily prepared in four steps from 167, opens the way to useful dienes. While 558 reacts with either phenol or sodium benezenesulfinate in the presence of palladium(O) and triethylamine to produce the expected ( , E)-dienes 559 and 560 respectively, the reaction of 558 with dimethylmalonate under neutral conditions provides the y-alkylated product 561 with 98% diastereoselectivity together with the minor 8-alkylated product (7 = 6 1) [181] (Scheme 124). 

Kang S, Park D, Jeon J, Rho H, Yu C. Highly regioselective palladium-mediated substitution of allylic and dienylic cyclic carbonates. Tetrahedron Lett. 1994 35 2357-2360. 

Nucleophilic addition to these complexes is a little less predictable than for the dienyliron systems. For example, the nucleophiles studied add to C-3 of the acyclic dienyl ligand in (224), but to C-l of the cyclic system (225). Alkyllithiums add both to the cyclohexadienyl ligand, e.g. (227) gives (229), and to the cyclopentadienyl ligand, followed by interligand hydrogen transfer to give, e.g. (228). However, the fact that a hindered, very basic alkyllithium adds to a sterically hindered dienyl terminal carbon and does... 

Another interesting reaction is the Pd-catalysed /i-dccarbopalladation of 4-vinyl cyclic carbonates 382 to afford dienyl aldehydes or ketones 384. The 2-oxa-l-... 

Active Figure 15.5 An orbital view of the aromatic cyclopenta-dienyl anion, showing the cyclic conjugation and six tt electrons in five p orbitals. The electrostatic potential map further indicates that the ion is symmetrical and that all five carbons are electron-rich (red). Sign in at www.thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

The photoindueed 1,7-cycloaddition of carbon monoxide across the divinyl-cyclopropane derivative 32 yields the two cyclic dienyl ketones 34, via the ferracyclononadiene intermediate 33 [18]. (Scheme 11) cyclopentene rearrangement. The dienylcyclopropane 35 is capable of forming the complex 36, followed by ring enlargement to 37 [19]. 1,1-Dicyclopropylethylene 29 is also converted to the 1-cyclopropyl-1-cyclopentene 38. The additional functionality of vinylcyclopropanes is necessary to serve as a 7t-donor... 

Acid mediated elimination of cyclic (dienyl ether)- and (dienol)Fe(CO)2L complexes leads to the formation of (cyclodienyl)Fe(CO)2L cations (equation 26 and 27) . Protonation of (pentadienol)- or (pentadienyl ether)Fe(CO)3 complexes generates the corresponding (pentadienyl)Fe(CO)3+ cations 167 (Scheme 41). Lillya and coworkers have demonstrated that ionization of the hydroxyl substituent occurs with anchimeric assistance from iron, and that isomerization of the initially generated transoid pentadienyl cation 168 to the more stable cisoid cation occurs with retention of configuration about the Cl—C2 bond . The in situ generated transoid pentadienyl cations may also undergo reaction with heteroatom, hydride or carbon nucleophiles to afford substituted ( , -diene)Fe(CO)3 products (169) . Acyclic (pcntadicnyl)MCp cations (M = Rh, Ir) may be prepared by acidic dehydration of (dienol)MCp complexes. ... 

A boron-tethered (C-B-O) intramolecular Diels-Alder (IMDA) approach has been used to prepare cyclic alkenyl boronic esters 140 (Scheme 19). Thus, reaction of 2equiv of the dienyl alcohol 138 with 137 in THF, in the presence of molecular sieves, provides the corresponding IMDA precursors 139. The IMDS reaction was then accomplished at 190 °C in a toluene solution, with 5 mol% of 2,6-di-fer7-butyl-4-methylphenol as a free radical inhibitor. Transformation of the carbon-boron bond in 140, using standard organoborane reactions, can then afford a variety of functionalized cyclohexene derivatives <1999JA450>. 

The most typical 5e dienyl ligands are five-, six-, and seven-membered cyclic and some acyclic hydrocarbons/The simplest ligand of this type is cyclopentadienyl in which all carbon atoms are equivalent and lie in the same plane. 

It has been reported that a retro-oxidative cyclization process proceeds in catalytic C-C bond cleavage reactions. For example, a six-membered cyclic allylic carbonate 38 underwent a palladium-catalyzed decarboxylative C-C bond cleaving reaction to afford dienyl aldehyde 40 (Scheme 7.12) [15]. It is proposed that oxidative addition of the allylic carbonate to palladium(O) followed by elimination of carbon dioxide generates the palladacycle 39. Subsequent retro-oxidative cyclization produces the diene and aldehyde functionalities. 

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