Alkenyl acids, reaction with

The key step in the total synthesis of rhizobitoxine is the Pd-catalyzed exchange reaction of the methyl alkenyl ether moiety in 4 with the functionalized alcohol, although the yield is low[3]. The enol pyruvate 6 (a-ethoxyacrylic acid) is prepared by the reaction of methyl a-methoxyacrylate or a-methoxy-acrylic acid (5) with ethanol catalyzed by PdCl2(PhCN)2 at room temperature in the presence of CuCli and NaH2P04[4],... 

In the olivanic acid series of carbapenems the ( )-acetamidoethenyl grouping can be isomerised to the (Z)-isomer (19) (22) and reaction with hypobromous acid provides a bromohydrin that fragments to give a thiol of type (20) when R = H, SO H, or COCH. The thiol is not isolated but can react to provide new alkyl or alkenyl C-2 substituents (28). In the case of the nonsulfated olivanic acids, inversion of the stereochemistry at the 8(3)-hydroxyl group by way of a Mitsunobu reaction affords an entry to the 8(R)-thienamycin series (29). An alternative method for introducing new sulfur substituents makes use of a displacement reaction of a carbapenem (3)-oxide with a thiol (30). Microbial deacylation of the acylamino group in PS-5 (5) has... 

Organomercury reagents do not react with ketones or aldehydes but Lewis acids cause reaction with acyl chlorides.187 With alkenyl mercury compounds, the reaction probably proceeds by electrophilic attack on the double bond with the regiochemistry being directed by the stabilization of the (3-carbocation by the mercury.188... 

The Lewis acid catalyst 53 is now referred to as the Narasaka catalyst. This catalyst can be generated in situ from the reaction of dichlorodiisopropoxy-titanium and a diol chiral ligand derived from tartaric acid. This compound can also catalyze [2+2] cycloaddition reactions with high enantioselectivity. For example, as depicted in Scheme 5-20, in the reaction of alkenes bearing al-kylthio groups (ketene dithioacetals, alkenyl sulfides, and alkynyl sulfides) with electron-deficient olefins, the corresponding cyclobutane or methylenecyclobu-tene derivatives can be obtained in high enantiomeric excess.18... 

The most synthetically valuable method for converting alkynes to ketones is by mercuric ion-catalyzed hydration. Terminal alkynes give methyl ketones, in accordance with the Markownikoff rule. Internal alkynes will give mixtures of ketones unless some structural feature promotes regioselectivity. Reactions with Hg(OAc)2 in other nucleophilic solvents such as acetic acid or methanol proceed to / -acetoxy- or /i-mcthoxyalk-enylmercury intermediates.116 These intermediates can be reduced to alkenyl acetates or solvolyzed to ketones. The regiochemistry is indicative of a mercurinium ion intermediate which is opened by nucleophilic attack at the more positive carbon that is, the additions follow the Markownikoff rule. Scheme 4.7 gives some examples of alkyne addition reactions. 

A more comprehensive study on the behavior of 5-acetylenic iodides in the presence of zinc was later reported21 and clearly revealed that when iodide 14 was treated with acid-washed zinc (pre-treated with Mel for activation and removal of traces of moisture) in a mixture of benzene and DMF, the acyclic organozinc iodide 21 and the cyclic vinyl iodide 22 were both produced. The amount of 22 increased significantly when the reaction mixture was sonicated rather than stirred or if a zinc-copper couple was used. The accumulation of compound 22 was consistent with its inability to be converted to an alkenyl organozinc species by reaction with metallic zinc under these conditions. However, no substantial cyclization of the open-chain organozinc 21 was observed. The formation of the five-membered ring compound 22 was attributed to a free-radical process... 

A variety of fluorinated alkenyl zinc reagents such as CF2=CFZnCl, CF2=CHZnCl, E and Z-RCF = CFZnCl have been prepared by the first method (Scheme 54). In the presence of palladium catalyst, these fluorinated alkenyl zinc reagents undergo cross-coupling reactions with aryl iodides, vinyl iodides, acid chlorides and 1-iodo-l-alkynes to give the corresponding fluorinated alkenyl derivatives [127, 146-153], which have been utilized in the synthesis of fluorinated codlemones [154]. Typical examples are outlined below (Scheme 55). 

The coupling reaction with active halides such as allyl halides or acid chlorides catalyzed by cuprous halides afforded the corresponding alkenylated compounds [131,167,168] (Scheme 57). 

A practical method for preparation of fluorinated alkenyl copper reagents has been recently developed from cuprous halides metathesis of the corresponding zinc or cadmium reagents [180]. These copper reagents exhibit excellent stability at room temperature and undergo a variety of coupling reactions with methyl, allyl, vinyl, aryl and acid halides [180] (Scheme 63). More recently, preparation of cyclic perfluoroalkenyl copper reagents has been reported by the same route [156-158]. 

Chromium alkenyl Fischer carbenes have been shown to undergo a 3 + 2-cyclization with allenes under Rh(I) catalysis and a CO atmosphere, yielding 2-alkylidenecyclo-pentanone (54) after acidic hydrolysis.46 Reactions with electron-rich allenes are carried out with a neutral rhodium complex whereas electron-poor allenes require a... 

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