Allylic cyclic carbonates

Ethylene reacted with iodonium salts in the presence of a palladium catalyst and a base to afford directly 1,2-bis arylated products (stilbenes). Styrene underwent arylation under similar conditions [44], Allylic cyclic carbonates were efficiently phenylated by diphenyliodonium tetrafluoroborate because of the mild conditions, no ring opening occurred, as was the case when iodobenzene was used. 

Using this method, several mesogen diacetylenes were obtained [49]. Palladium-catalysed coupling of an allylic cyclic carbonate with 1-pentynyl phenyliodonium tetrafluoroborate to give an enyne was highly successful [50]. Alkynyl iodonium triflates and lithium salts of diethyl 2-[(diphenylmethylene)amino]malonate were used for the preparation of alkynyl-a-amino acid derivatives, e.g. [51] ... 

Allylic substitution of allylic cyclic carbonates with PhSH or PhOH is also catalyzed by (C5H5)Ru(PPh3)2Cl complex (5 mol%) to afford ( )-allylic alcohol and ery-thro-/3-hydroxy thiophenoxide or phenoxide, respectively, where the substitution proceeds by the external attack of a Jt-allylruthenium complex by nucleophiles with an overall net retention of configuration (Eq. 5.35) [59]. 

Chiral allylic cyclic carbonates such as 551 or 552 undergo excellent regioselective alkylation reactions with soft nucleophiles in the presence of palladium(O) in refluxing THF to provide ( )-allylic alcohols. The reaction of 4-0-benzyl-2,3-isopropylidene-L-threose (167) with the appropriate ylid, followed by deprotection of the isopropylidene ring with acidic resin and cyclic carbonate formation, provides a good overall yield of either 551 or 552. Ring opening with diethyl malonate in the presence of tetrakis(triphenylphosphine)palladium(0) provides in excellent yield the allylic alcohols 553 or 554, where the diastereoselectivity exceeds 99%. This reaction represents an efficient method of 1,3-chirality transfer [180] (Scheme 122). 

These chiral allylic cyclic carbonates are also capable of reacting with carbon, oxygen, or sulfur nucleophiles to provide products whose regio- and diastereoselectivities depend on the nature of the nucleophile. The reaction of 551 with phenol in the presence of palladium(O) and triethylamine provides in 79% yield 555, whereas similar reaction with sodium benzene-sulfinate furnishes the ( )-allylic alcohol 556 in 80% yield. However, sodium thiophenoxide, under conditions that do not lead to catalyst poisoning, attacks proximal to the oxygen atom with inversion to afford the threo-P-hy oxy sulfide 557 in 74% yield. This reaction is not observed in the absence of a palladium catalyst [181] (Scheme 123). 

Other authors have used the combination of allylic carbonates with hydride sources,with particular success in syntheses of the natural pigment t/Z-shikonin and of (+)-a-allokainic SicidP ° Reduction of allylic cyclic carbonates has been... 

J. PALLADnJM(0)-CATALYZED REACTIONS OF ALLYLIC CYCLIC CARBONATES... 

A few Pd(0)-catalyzed reactions of aUyUc carbonates cannot be classified under Sects. A-O. Cationic Tj -allylpalladium complexes can be reduced by tin(II) chloride to afford a tin-allyl intermediate provided with nucleophilic reactivity (umpolung), which reacts with carbonyl groups (Scheme 62). Tm(II) chloride has been used by Masuyama and co-workers in Pd(0)-catalyzed reduction of aUylic carbonates,allylic cyclic carbon-ates, and even allylic alcohols,followed by reaction with carbonyl compounds. Related results with cyclic carbonates have been reported by Kang and co-workers Diethylzinc and samarium(II) iodide have been used as the reducing reagent. Protona-tion of the allylsamarium intermediate gives overall reduction of the C—O into C—H bond.f ... 

Highly regio- and stereoselective 4a-deuteration in steroids is possible by the hydrogenolysis of the cyclic allylic /3-carbonate 628 with NaBD4. the extent of 6a-deuteration is only 3%[393],... 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Ni(cyclam)]2+ was shown to be an efficient electrocatalyst for the intramolecular cyclization-carboxylation of allyl or propargyl-2-haloaryl ethers,200 and for the synthesis of cyclic carbonates from epoxides and carbon dioxide.201... 

A study of the Pd-catalyzed resolution of allylic substrates with thiols was undertaken to see whether they could function as nucleophiles [11]. The cyclic carbonates rac-laa and roc-lba and the acyclic carbonates rac-3aa and rac-3ba were selected as substrates and 2-pyrimidinethiol as nucleophile (Schemes 2.1.4.5 and 2.1.4.6). The reactions of carbonates rac-laa and rac-lba with 2-pyrimidinethiol... 

As shown by Table 2.1.4.7, the highly enantio-enriched cyclohexenyl and cyclo-heptenyl sulfones 2aa and 2ba, respectively, were obtained in high yields by using Pd(0)/L (1.5 mol%) and BPA (4.5 mol%) (entries 1 and 2). In the case of the eight-membered cyclic carbonate roc-lca the selectivity of the kinetic resolution was so high that even after a prolonged reaction time the conversion of the allylic... 

At this point, there were two problems in selective alkene functionalization to be addressed. Although all attempts at oxidation of the cyclopentene failed, intramolecular hydrosilylation proceeded smoothly, to give 13. On exposure of the derived cyclic carbonate to HgfOjCCF,), the cyclononene then underwent allylic oxidation, to give 14. 

The palladium-catalyzed fixation of C02 is also a useful method for the synthesis of CCs, with the first such example using vinyl-substituted epoxides and a palladium catalyst [Pd(PPh3)4/PPh3] having been reported independently by both Fujinami and Trost [147, 148]. Here, the carbonate is produced via the formation of a first tr-allyl-palladium intermediate (I) this then fixes C02 to form a second tr-allyl-intermediate (II) that produces vinyl-substituted cyclic carbonates (Scheme 7.8). 

Various unsaturated compounds, such as CO2, isocyanates and aldehydes, undergo Pd-catalysed cycloaddition with vinyl epoxides. Reaction of CO2 with 127 affords cyclic carbonates 128 with retention of the configuration at C(3), offering a method of cis hydroxylation of epoxides [66], and has been used for the synthesis of the side-chain unsaturated (—)-exo-brevicomin (129) [67], The tetrahydrofuran 131 was prepared by [3+2] cycloaddition of activated alkenes such as benzylidene malononitrile (130) with vinyl epoxide via Michael addition and allylation [68],... 

Beckwith has observed moderate diastereoselectivity in this reaction involving cyclic systems. The cyclizations of allyl and homoallyloxycarbonyloxy radicals are potentially useful as radical based alternatives for an overall oxidation or hydrolysis of a double bond, and also various further transformations of the cyclic carbonates can lead to synthetically useful products.62b In contrast, simple alkoxycarbonyloxy radicals 91a add intermolecularly to ethyl vinyl ether to give, ultimately, carbonates of glycoaldehyde derivatives 91b, Scheme 37.62a... 

Lactone carbaldehyde 143 was treated with vinyl iodide in the presence of chromium(ll) chloride and Me2SO to provide allyl alcohol 144 in 59% yield as a 2 1 diastereomeric mixture (Scheme 26 major isomer shown) <2000CC631>. Further deprotection, conversion into cyclic carbonate, and final treatment with dimethyltitanocene provided /rawr-fused bicyclic lactone 145 in 25% yield. 

The transition metal-catalyzed allylation of carbon nucleophiles was a widely used method until Grieco and Pearson discovered LPDE-mediated allylic substitutions in 1992. Grieco investigated substitution reactions of cyclic allyl alcohols with silyl ketene acetals such as Si-1 by use of LPDE solution [95]. The concentration of LPDE seems to be important. For example, the use of 2.0 M LPDE resulted in formation of silyl ether 88 with 86 and 87 in the ratio 2 6.4 1. In contrast, 3.0 m LPDE afforded an excellent yield (90 %) of 86 and 87 (5.8 1), and the less hindered side of the allylic unit is alkylated regioselectively. It is of interest to note that this chemistry is also applicable to cyclopropyl carbinol 89 (Sch. 44). 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

The Pd-catalyzed coupling reactions of cyclic allyl chlorides, carboxylates and epoxides " with alkenyl-Al, alkenyl-Sn and aryl-Sn reagents proceed with inversion of configuration of the allylic sp> carbon centers (equations 206-208). 

Hydrogenolysis. Deoxygenation of l-alkene-3,4-diols with transposition of the double bond is accomplished via the cyclic carbonates. Heating the latter compounds with RuH2(PPhj)4 and HCO NH in THF leads mainly to the ( )-allylic alcohols. Some saturated alcohols are also formed. 

Alfylations. A direct preparation of allyltin reagents from allyl halides is accomplished by treatment with SnCl. Allytributylstannane is activated by SnClj in MeCN for reaction with carbonyl compounds and imines. Allylic alcohols and cyclic carbonates can also be used as allylating agents for amines and aldehydes, respectively. 

The most common nucleophiles employed in the allylic alkylation are soft species such as malonate esters. However, Trost and Schroeder have discovered that high ees can be achieved in the addition of cyclic lithium enolates using ligand (10.54) with one equivalent of trimethyltin chloride, which may act to soften the nucleophilic species by transmetaUation to the tin enolate. Enantioselective additions of nonstabilised ketone enolates can also be achieved using an alternate palladium-catalysed decarboxylation protocol. In this approach an allyl 3-ketoester (10.72) or allyl vinyl carbonate (10.73) undergoes decarboxylation in the presence of Pd(0) to... 

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