Carbonylation vinylcyclopropanes

With the low-valence iron pentacarbonyl, vinylcyclopropanes 22 are thermally transformed to the diene re-complexes, the (1,3-trans-pentadiene)iron carbonyl complexes 23, through bond fission, 1,2-hydrogen shift, and stereoselective coordination [15]. (Scheme 9)... 

Vaska s complex catalyzed the transformahon of aUenylcyclopropane into 2-alkenylidenecyclohex-3-enone under conditions of pressurized CO (Scheme 11.25) [38]. In this reaction, the jr-coordination to internal oleflnic moiety of the aUene brings the metal closer to the cyclopropane ring. Release of the cyclopropane ring strain then facilitates the oxidative addition of vinylcyclopropane moiety along with C-C bond cleavage, such that metallacyclohexene is obtained a subsequent carbonyl insertion and reductive elimination then provides the product Hence, the reaction can be recognized as a [5+1] cycloaddition of vinylcyclopropane and CO. 

Since the pioneering work by Sarel and co-workers on the iron carbonyl promoted transformation of vinylcyclopropanes and related compounds [1], a variety of transition metal complexes have been examined to achieve effective activation of the vinylcyclopropane-cyclopentene rearrangement which usually requires pyrolytic conditions. These reactions have been applied to natural product synthesis in some cases and have already been reviewed in several excellent articles [2-4]. 

Other methods leading to ring enlargement utilize low-valent iron complexes such as Fe(CO)5, as was shown by Taber and coworkers in the ring expansion of vinylcyclopropane derivatives 55 under carbonylating conditions to give the cyclo-hexenone derivatives (Scheme 9.43) as a 5.9 1 mixture of the 2,5- (56) and the constitutional isomer, the 2,6-substituted cydohexenones [101, 102],... 

Alkyne-vinylcyclopropanes, metal-catalyzed [5+23-cycloadditions, 10, 605 Alkynides, with tungsten carbonyls, 5, 666 Alkynoic acids, stannylmetallation, 9, 374 Alkynoles, hydration-dehydration reactions, 6, 841... 

Table 7 Reactions of Vinylcyclopropanes and a,P-Unsaturated Carbonyl Compounds Catalyzed by...

Reactions of phenylthiocyclopropyl lithium with alkyl halides and epoxides have also been reported to deliver products opened to a variety of carbonyl derivatives jS-(l-Phenylthio)cyclopropyl enones have been prepared by using lithium salts of a-hydroxymethylene ketones as electrophiles and dehydrating with acid (equation 110). Rearrangement to cyclobutanones occurs with trifluoroacetic acid, whereas thermal vinylcyclopropane-cyclopentene expansion sometimes gives mixtures of regioisomers . 

The formation of pyrroles by the reaction of the cyclopropylketimine (63) with HBF4 has been studied from a mechanistic point of view using 3-chloropropionyl chloride enriched with at the carbonyl carbon atom The C-NMR spectrum of the pyrrole formed from the cyclopropyl ketimine (63) shows enhancement of the peak at the 5-carbon in accord with mechanism A outlined in Scheme 27. Operation of process B analogous to the vinylcyclopropane rearrangement 63a would have led to enrichment at the 3-carbon of the pyrrole product. 

An alternative strategy for achieving asymmetric control may be by covalent attachment of a chiral auxiliary to the carbenoid. This strategy has so far met with rather limited success in cyclopropanation reactions (see eq. (3) for a similar palladium-catalyzed reaction). However, the use of a-hydroxy esters as chiral auxiliaries with stabilized rhodium(II) vinylcarbenoids allowed entry into both series of enantiomeric vinylcyclopropanes with predictable stereochemistry. Optical yields are fair to excellent [14] and the outcome of the reaction was rationalized on the basis of interactions between the carbonyl oxygen of the chiral auxiliary and the carbenoid carbon. The strategy led to an efficient synthesis of optically active hydroxy vitamin D3 ring A [28]. 

Table 10. Synthesis of Vinylcyclopropanes from Ethyl 2-Bromobut-2-enoates and a./J-Unsaturated Carbonyl Compounds ...

A novel concept for performing one-pot cyclopropanations of a, 9-unsaturated carbonyl compounds, consists of conjugate addition of an appropriate phenylthio-stabilized organolithium compound followed by treatment of the resulting enolate anion with copper(I) trifluoro-methanesulfonate. The cyclopropanes generated by this procedure can be simply substituted, for example, by silyl- and sulfur-bearing groups, or they can be vinylcyclopropanes (Table 13). 

A vast number of vinylcyclopropanes have been synthesized by performing condensation reactions between nucleophilic reagents and cyclopropanecarbaldehydes and cyclopropyl ketones. A range of reaction conditions have been employed, but in most syntheses the carbonyl function has been converted to an alkene moiety by using a Wittig reagent. 

On the other hand, isolable transition-metal-bound cyclopropyl systems can also be used in coupling reactions. Thus bis(cyclopentadienyl)bis(cyclopropyl)titanium reacted, in a Tebbe-type transformation, with carbonyl compounds to give methylenecyclopropanes 3 and with alkynes to form vinylcyclopropanes 4 via carbonyl olefination. ... 

Alkyl-allyl complexes of isomeric systems can be interconverted and thus be used in isomerization of vinylcyclopropanes. Ethyl 4-azabicyclo[5.1.0]octa-2,5-diene-4-carboxylate (20) reacts with pentacarbonyliron to give complex 21, which photochemically rearranges to complex 23. Carbonylation of both products 21 and 23 leads to ethyl 9-oxo-2-aza-bicyclo[3.3.1]nona-3,7-diene-2-carboxylate (22). While complex 21 upon heating regenerates the starting material, complex 23 gives the isomeric product 24. In contrast to iron, with rhodium only the endo-complex 25 is formed. ... 

In a similar fashion, diethyl cyclopropane-1,1-dicarboxylate (4) reacted with lithium dialkyl-cuprate to give the corresponding malonates S in high yields. Byproducts could be formed by the attack of the organometallic reagent at the carbonyl function. With diethyl 2-vinyl-cyclopropane-1,1-dicarboxylate (6), a preference for the 1,7-addition of the dialkylcuprate was found. Similar observations were made with 1-acetyl- (9,R = Me) and 1-benzoyl-2-vinylcyclopropane (9, R = Ph) when reacted with various dialkyl- and diphenylcuprates and with a vinylcyclopropanedicarboxylate fragment incorporated into a polycyclic system to yield compound 11. ... 

Vinylcyclopropanes can react with pentacarbonyliron to give two different types of addition products i) (diene)tricarbonyliron 7r-complexes as the result of ring opening, hydrogen shift, and complexation ii) cyclohexenones by photoinduced carbonyl insertions across the vinyl-cyclopropane system. 

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