Allyl phosphates, carbonylation

Allylic phosphates are used for carbonylation in the presence of amines under pressure. Carbonylation of diethyl neryl phosphate (389) affords ethyl homonerate (390), maintaining the geometric integrity of the double bond[244]. The carbonylation of allyl phosphate in the presence of the imine 392 affords the /3-lactam 393. The reaction may be explained by the formation of the ketene 391 from the acyl phosphate, and its stereoselective (2 + 2] cycloaddition to the imine 392 to give the /3-lactam 393(247],... 

The simple procedure for the carbonylation of allyl halides has been extended in the high yielding solid-liquid two-phase conversion of allyl phosphates into amides (60-80%) under the influence of a rhodium carbonyl cluster in the presence of primary or secondary amines (Scheme 8.8). A secondary product of the reaction is the allylamine, the concentration of which increases as the pressure of the carbon monoxide is reduced, such that it is the sole product (ca. 80%) in the absence of carbon monoxide [28],... 

The palladium-catalyzed carbonylation reaction of allyl diethyl phosphate, in the presence of imines, gives either cis- or rraws-3-vinyl-/J-lactams, in high yields and in a stereoselective fashion (equation 160)574,575. The reaction is a [2 + 2] cycloaddition process which occurs under simple and mild conditions and has significantly more potential than the reaction of imines with ketenes (due to the more forcing conditions that are usually required to form the ketene intermediates). This reaction, however, only proceeds in low yield if the allyl phosphate is replaced with allyl acetate576. 

A closely analogous Pd-catalyzed carbonylative bicylization of 2-(pro-pargyl)allyl phosphates reported recently [147] can readily be explained in terms of a Type III Ac-Pd mechanism shown in Scheme 61, even though the authors of this paper additionally proposed an alternate ketene-alkyne bicy-clization mechanism also shown in Scheme 61. 

Allylic halides are not as readily accessible as allylic alcohols or their ester derivatives. Thus, the requirement that allylic halides must be used as precursors for carbonyl addition reactions in conjunction with magnesium and other similar reductants is a severe restriction limiting the convenience of these routes to homoallylic alcohols. In this regard, samarium diiodide can be used to great advantage, because substrates other than allylic halides are suitable precursors for such transformations. For example, allylic phosphate esters have been reported to couple with carbonyl substrates in the presence of Smh (equation 15). Since esters and nitriles are unreactive under these conditions, the Smh-mediated process is likely to be more chemoselective than those promoted by magnesium or lithium. 

Allylic substitutions. Substitution of an allylic phosphate with an alkoxycarbonyl group, formation of oxazolidine derivatives, and vicinal C-allylation/carbonylation of... 

Allylic barium reagents prepared in this way can realize highly a-selective reactions with different electrophiles, e.g. cross-coupling reactions with allylic halides or allylic phosphates, additions to carbonyl compounds or imines, and ring opening of epoxides. A selective Michael addition reaction with an a,/ -unsaturated cy-cloalkanone can also be performed by use of an allylic barium reagent. 

Rhodium carbonyl clusters. 13, 288 15. 3j Hydrogenation. Rh6(CO)i6 catalyzes compounds with CO and H2O at atmospheric Homologations. Hydroformylation of ated by Rh4(CO)i2. Homologous carboxylic ai obtained from allyl phosphates. ... 

Homoallyttc alcohols. The reaction of carbonyl compounds with allylic halides in the presence of CrCl shows a difference in stereoselectivity from that with allylic phosphates. Stereoisomers with opposite configuration at the quartemary center can be obtained by using either of the two ( )- or (Z)- allylic precursors. 

Vinyl ketene (392) is generated by the carbonylation of the allyl phosphate 390 in the presence of a base as shown by 391. A useful application of the ketene formation is the synthesis of -lactam skeleton by [2 -I- 2] cycloaddition of the ketene with imines. Thus, reaction of the imine 393, derived from vicinal dicarbonyl compounds, with the ketene 392 afforded cw-lactam 394 [152], On the other hand, the transAacism 397 was obtained by the carbonylation of the allyl phosphates 395 in the presence of the imine 396 derived from aldehyde [153]. 

Other organic processes facilitated by metal carbonyl clusters include a palladium carbonyl catalysed Diels-Alder reaction the selective reduction of aromatic nitro compounds using rhodium and ruthenium phosphine-carbonyls aza- and oxa-carbonylations of allyl phosphates by rhodium carbonyls Michael reactions of alkoxy-alkenones using iron... 

Allyl sulfones and phosphates also undergo the allylation of carbonyl compounds via umpolung of 7r-allylpalladium with diethylzinc (Scheme 18). Allyl sulfone is less reactive and the reaction is performed at higher temperature. a,a-Dimethylallyl sulfone reacts with benzaldehyde at the tertiary carbon, while y.-y-dimethylallyl sulfone is unreactive and recovered under similar conditions.Allyl phosphate shows an interesting regioselectivity... 

Allyl phosphates also react with imines under similar carbonylative conditions to yield lactams, but the reaction mechanism involves a [2 + 2] cycloaddition of the imine and a ketene generated by decomposition of an acylpaUadation intermediate (for this type of reaction, vide infra, Sect. 

The most prominent use of ketenes is for [2 + 2] cycloaddition with imine for the construction of /3-lactam skeleton. When the Y group in Scheme 1 is vinyl or aryl group, the deprotonation of the activated a-proton is highly facilitated. In this context, the carbonylation of some allylic derivatives, for example, allyl bromide, allyl acetate, allyl phenyl ether, allyl methyl carbonate, allyl phenyl sulfone, and allyl phosphate, documented to form TT-allylpalladium intermediates is examined. It is interesting to note that only phosphate undergoes the cycloaddition to produce /3-lactam. The characteristic dependency of the stereochemistry on the reaction conditions, being contrary to the results in the usual base-induced cycloaddition is also intriguing. Scheme 2 presents the... 

The catalytic carbonylation of allyl phosphate, a new ketene equivalent, provides a convenient route to a series of /S-lactams bearing useful substituents at the positions relevant for further structural modifications with unique stereocontrol. 

As described in the preceding subsection, the carbonylation of allyl phosphate forms vinyl ketene or its equivalent by the removal of a-proton of allylacylpalladium (Scheme 6, Route A). The same reactive species should be released by the deprotonation of y-proton of vinylacylpalladium intermediate (Route B). 

Araki and Butsugan have recently described the lithium-mediated allyla-tion of carbonyls by means of an allylic phosphate anion [91]. 

The carbonylation of allylic phosphates followed by elimination may form a vinylic ketene intermediate, which may further undergo [2+2]-cycloaddition with 2-aryl-1,3-thiazines to afford bicyclic /3-lactams highly diastereoselectively (eq 8). ... 

The [2+2] cycloaddition of a ketene and an imine leading to P-lactams can be accomplished using palladium catalysis. Starting from an allyl phosphate or allyl chloride (see also 1), carbonylation with carbon monoxide lead to an intermediate ketene that cycloadds to imines to form the desired P-lactams (Scheme 5-176). ... 

Pd(Ph3P)2Cl2(Bu3SnH, benzene) or cobalt carbonyl. The palladium method cleaves allyl esters, propargyl phosphates, and propargyl carbamates as well. 

Allylic acetates and phosphates can be readily carbonylated.248 Carbonylation usually occurs at the less-substituted end of the allylic system and with inversion of configuration in cyclic systems. 

The reaction of but-l-en-3-yl diethyl phosphate with diethylamine produces N,N-diethylpent-3-enamide (86%), indicating that a Ji-allyl complex is involved in the carbonylation reaction. No isomerism to the a,p-unsaturated amides was observed. 

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