Cycloalkenylation reagent

Reactions of chiral cycloalkenyl reagents with rigid ketones affords products with a high degree of stereodifferentiation ... 

Starting with 2-ethynylaniline, Cacchi and co-workers have prepared 2-aryl and 2-(cycloalkenyl)indoles by coupling followed by cyelization[7]. The reagents for the coupling step are Pd(PPh3)3. Cul Et2NH. The cyclization is... 

C is-fused tetrahydrofurans are produced when 2-cycloalkenyl-substituted ethanol derivatives are cy-clized via 5-exo ring closure (equation 14 and Table 5). The related 1-cycloalkenyl alcohol systems also yield cri-fused tetrahydrofurans upon reaction with phenylselenyl reagents, similar to their carboxylic acid analogs (see equation 12).60 A sulfoetherification to a fused ring tetrahydrofuran from a system with an exocyclic methylene provided an 86 14 ratio of cis- and frans-fused isomers.61... 

Carbethoxycyclopropyltriphenylphosphonium fluoroborate (475) proves to be an excellent reagent for cycloalkenylation of carbonyl compounds. Reaction of p-kcio esters (as their sodium enolates) smoothly produces cyctopentene diesters (602) (equation 213). The mechanism can be most simply viewed as a nucleophilic attack of the enolate on the cyclopropane ring to produce a stabilized ylide, which rapidly cyclizes to the... 

The ylid 371 prepared by treating cyclopropyltriphenylphosphonium bromide (with lithium diisopropylamide (LDA) produces a useful synthon on reaction with ethyl chloroformate . The fluoroborate salt (372) was shown to be an excellent reagent for cycloalkenylation of carbonyl compounds. The ylid was used successfully in the total synthesis of Spirovetivanes. ... 

Phosphonium chloride 2 is readily hydrolyzed in alkaline medium giving cyclopropanecarb-oxylic acid (4), while the phosphonium tetrafluoroborate 3 is an excellent reagent, for the cycloalkenylation of carbonyl compounds, e.g. -0x0 esters, or can be utilized for the construction of functionalized 2-pyrrolines (e.g. 7) from imides. A similar reaction with the sodium salts of cyclic imides gives access to ethyl l,2,5,6-tetrahydro-3-oxo-3//-pyrrolizine-7-carboxylate (6, n = 1) and ethyl 2,3,5,6,7,8-hexahydro-5-oxoindolizinecarboxylate(6, n = Other transformations include the conversion into 2,3-dihydrofurans 8" and spiroketo ester... 

Cycloalkenyl sulfides 10 are converted into bicyclo[n.2.0] alkane compounds with almost complete enantioselectivity by the reaction with the fumaric or acrylic acid derivatives 2a,c as listed in Scheme 8 and Table 3. As the reactivity of 10 is not as high as that of acyclic alkenyl sulfides, the use of an equimolar amount of the chiral titanium reagent is required to attain a good chemical yield in some cases. Diastereoselectivity is generally excellent and no ene product is detected. 

Vinyl Grignard reagents can also be used as the nucleophiles. For example, a series 1,3-bis(l -cycloalkenyl)benzenes 630 have been prepared via the tandem aryne sequence in reasonable yield. Similarly, trimethylsilyl vinyl Grignard 492 converts 622, via 631, to indenone 632 in which the three halogens have been replaced by three functionally differentiated adjacent carbons. ... 

The 2-chloro(perfluoro)cycloalkenylzinc reagent (472) reacts with thiophene carboxylic acid chlorides in the presence of CuBr to form the ketones (473) in excellent yields. The reaction is probably mediated by the corresponding 2-chloro(perfluoro)cycloalkenyl copper <91JCS(P1)1601>. 

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