Allyl carbonates stereoselective

Pd(0)-catalyzed hydrogenolysis of vinylepoxides offers an attractive regio- and dia-stereoselective route to homoallylic alcohols (Scheme 9.36) [104, 155, 156]. Thus, hydrogenolysis of ( ) olefin 88 affords syn isomer 89 with inversion of configuration at the allylic carbon, while subjection of (Z) isomer 90 to identical reaction conditions results in the anti isomer 91. The outcomes of these reactions are ex-... 

Substituted (5R,6A,)-6-(dimethyl(phenyl)silyl)-2-phenyldihydropyrazolo[l,2- ][l,2,4]triazole-l,3(2//,5//)-dione 716, synthesized via the [3+2] annulation of a-substituted allylic silanes 715 with PTAD, were oxidized to the corresponding hydroxy substituted urazoles 717. This work shows that allylsilanes with a single substituent at the allylic carbon undergo exclusive stereoselective [3+2] annulation (Scheme 114) <2007TL6671>. 

Two catalytic cycles are proposed to explain the difference in selectivity. In both cases, catalytic cycle is initiated by the oxidative addition of an alkynylstannane to nickel(O) species, leading to the formation of alkynylnickel(ll) complex 77 (Scheme 24).92 Then, an allene is inserted into the nickel(ll) complex in a manner which avoids steric repulsion with the butyl group to afford the anti-ir-a y complex 80. The carbometallation of the terminal alkyne can take place at the non-substituted allylic carbon of the corresponding syn-Ti-a y complex 78. The stereoselectivity is determined by the relative rate of the two possible insertion modes which depend on the ligand used. A bidentate... 

Trons-divinyl-pyrrolidines and -piperidines were prepared by sequential intermolecular and intramolecular aminations of bis-allylic carbonates (Scheme 9.21) [22aj. Due to double stereoselection, these reactions proceeded with high diastereoselectivity and enantioselectivity. 

In 1985, Warwel and Winkelmiiller reported a series of catalyst systems for the CM of either styrene or 4-vinylcyclohexane with unfunctionalized olefins (Scheme 9). Using heterogeneous catalyst systems of RceOy/ AI2O3, among others, the authors demonstrated that both a substrate s electronic and steric properties govern CM product selectivity. Unfortunately, as the stereoselectivities of these reactions were not reported, the effect of a secondary allylic carbon on olefin stereoselectivity was not determined. Nevertheless, the non-statistical product distribution obtained in these reactions constitutes the first example of a product selective CM reaction. 

Iodocyclization of trichloroacetimidates forms trans-1,3-oxazolines with moderate to good stereoselectivity (equation 118).234 Cyclizations of systems with internal double bonds (equation 119) generate 5-exo products only if the double bond has a (Z)-configuration (entries 2 and 3) or an oxygen substituent is attached to the allylic carbon (entries 3 and 4). Wc-153 ,i57b,254c... 

Another rapidly progressing field is that of multistep reactions which occur in ordered sequences chemo-, regio- and stereo-selectively on a transition metal species. To this end, it is necessary to delay release of the desired product until the whole series of steps has been completed competitive terminations (such as hydride elimination) must be prevented or must only occur at low rates compared to the main sequence. An example, reported by Chiusoli in the late 50s, is offered by the nickel-catalyzed synthesis of methyl 2,5-heptadienoate from 2-butenyl chloride, acetylene, CO and methanol. The reaction is chemo-, regio- and stereo-selective the four molecules react in the order shown in Equation A3.4 (chemoselectivity) the butenyl group attacks the terminal allylic carbon rather than the internal one (regioselectivity) and acetylene insertion leads to a Z double bond (stereoselectivity). 

The model correctly predicts (rationalizes) the observed preference for formation of Ae anti raAer than Ae syn product in the cycloaddition reactions of a wide variety of chiral allylic eAers, Aus successfully laying to rest years of frustrated discussion. - It also correctly predicts Aat as Ae size of R increases (Me - Ph < Et < Pr < Bu ), Ae preference for transition state structure (18 ) should increase leading to enhanced anti stereoselectivity (Table 15). At first, Ais prediction seems strange. However, once it is realized Aat, like Ae Felkin-Anh model for nucleophilic addition to a carbonyl, Ae outside position is actually more sterically demanAng Aan Ae inside, Aen Ae prediction is sensible on purely steric grounds. Thus, Ae angle d approach of Ae nitrile oxide oxygen to Ae alkene actually places it nearer Ae outside Aan Ae inside substituent located at Ae allylic carbon. ... 

Ruthenium-catalyzed carbonylations of allylic compounds [62] were described in Chapter 11. Here, ruthenium-catalyzed carbonylative cyclization of allylic carbonates with alkenes, not alkynes, which offers a new route to cyclopentenones is revealed [63]. Treatment of allyl methyl carbonate with 2-norbornene in the presence of 2.5 mol% [RuCl2(CO)3]2 and 10 mol% Et3N in THE at 120°C for 5 h under 3 atm of carbon monoxide gave the corresponding cyclopentenone, exo-4-methyltri-cyclo[5.2.1.0 ]dec-4-en-3-one, in 80% yield with high stereoselectivity exo 100%) (Eq. 5.37). 

Nucleophilic attack of the central carbon of allyl ligands represents an important access to metallacyclobutanes independent from cyclopropanes as precursors. This reaction pathway competes with the more common attack at one of the terminal allylic carbons. However, several examples of metallacyclobutane formation followed by release of cyclopropane products have been reported, especially with allyl complexes of palladium, platinum, and iridium as stable precursors or reactive intermediates in catalytic cycles. Detailed experimental (see below) and theoretical studies considering chemo-, regio- and stereoselectivity of the crucial reaction steps with respect to influence of the metal, ligands, substituents and reaction conditions are available. ... 

The InI-Pd(0)-promoted allylation of aldehydes with N-activated vinylaziridines or allylic acetates proceeds with regio- and stereoselectivity, irrespective of the chirality of the allylic carbon bearing the vinyl group, to provide sy ,syn-2-vinyl-l,3-amino alcohols with three contiguous chiral centers (Scheme 8.64) [90]. In a similar manner, 2-ethynyl-l,3-amino alcohols are synthesized from 2-ethynylaziridines (Scheme 8.65) [91]. 

Disparlure 18 is the sex attractant of the gypsy moth. The only functional group in disparlure is the epoxide and we need an alcohol somewhere if the stereoselective introduction of this group is to be done by AE. Our disconnection strategy7 is dominated by that thought - an alcohol must be introduced somehow at one of the allylic carbons in 19. 

Sn2 displacements. The opening of allylic carbonates and displacement reactions of chlorides are regio- and stereoselective processes. The thio unit of functionalized allyl thiazolin-2-yl sulfides is selectively removed during the reaction. ... 

Among a host of other phosphine-catalysed reactions in which the initial step is the formation of a reactive phosphoniobetaine intermediate by addition to a carbon-carbon double or triple bond are intramolecular cyclisations leading to benzobicyclo[4,3,0]-compounds, " cyclic ethers " and lactones,and a great many intermolecular reactions, e.g., a [3 -b 3]-annulation of modified t-butyl allylic carbonates and alkylidenemalonitriles to give cyclohexenes,phosphine- (and fluoride)- catalysed routes to 1,4-benzothiazepines from cyclic sulfenamides and alkynes, a [4- -3]-annu-lation of allylic carbonates with methyl coumalate to give functionalised bicyclo[3.2.2]nonadienes, the a-carbon addition of cyanide ion, generated in situ from cyanohydrins, to activated alkynes, and a stereoselective... 

A Ti/Pd bimetallic system catalyses allylation of carbonyl compounds, using allyl carbonates, and is particularly useful for ketones that are reluctant participants in many allylation protocols. Stereoselective intramolecular versions are also described. ... 

A combination of palladium-ene cyclization with carbonylation reactions is particularly attractive since it permits the stereoselective formation of four carbon-carbon bonds in a single process. In this reaction, 7r-allylpalladium complex 47 (Scheme 11) is formed from allyl carbonate 46 and Pd(0), and it is then converted into vinylpalladium complex 48 via palladium-ene cyclization. Carbonylation of 48 gives bicyclic compound 49, which is further reacted with carbon monoxide to give carboxylic acid 50. 

Studies reporting substituent effects on the palladium- and copper-catalysed Sonogashira coupling reaction between an aryl iodide and an alkyne the 5 2 allylic substitution reactions between benzyl amine and racemic allyl carbonates substituted with a j -X-Ph- group on C(l) in the presence of a Rh(15,15, 2/ ,2/ -tangphos)(COD)Bp4 catalyst the stereoselective 5 2 reactions between a-substituted linear 0-ketoesters and meta- and /Jura-substituted cinnamyl carbonates generating vicinal quaternary and tertiary stereocenters in the presence of an Ir-V-arylphosphoramidite catalyst, TBD, and LiOBu-t identity vinyl halide reactions the S N... 

Cozzi employed stereoselective CDC reactions promoted by DDQ and the MacMillan catalyst 133 (Scheme 8.65). Various compounds having a benzylic and/or allylic carbon can be converted into the corresponding C-C coupling products 134-137 in low-to-moderate yields with moderate-to-high enantioselectivities. 

He A, Sutivisedsak N, Spilling CD. Stereoselective synthesis of cyclic ethers via the palladium-catalyzed intramolecular addition of alcohols to phosphono allylic carbonates. Org. Lett. 2009 11 3124 3127. 

---