Cyclopentenes 1-sulfonyl

SULFONYL)M ETHYL] FUR AN AND 2-METHYL-3-[(PHENYLSULFONYL)METHYL]-2-CYCLOPENTEN-1-ONE (Benzene, [(2,3-dlbromO 1-propenyl)sulfonyl]>, Furan, 2-methyl-4-[(phenylsulfonyl)methyl]-, and 2-Cyclopenten-l-one,... 

A similar acceleration has most recently been observed in the rearrangement of vinylcyclopropanes of type (39 Scheme 8). This fluoride-mediated vinylcyclopropane-cyclopentene isomerization proceeds at -78 C to give (40) in 85% yield this is to date the mildest condition available. Two possible intermediates, the enolate anion (39a) or the diradical anion (39b), may be responsible for such acceleration in analogy to the enolate anion accelerated divinylcyclobutane rearrangement recently reported." The mechanism of this transformation is unclear but may involve anion acceleration similar to that observed in the rearrangement of sulfonyl anions derived from (42 Scheme 8). By comparison the thermolysis of (39) produced exclusively the endo isomer of (41) at 580... 

The nucleophile can be internally located on the vinylcyclopropane moiety as exemplified in the case of the anion-accelerated rearrangements of sulfonylvinylcyclopropanes of type 10. The resulting cyclopentenes can be further functionalized, through the agency of the sulfonyl group, in an overall four-step sequence from the starting diene. 

Subsequently, Shi and Li synthesized a more nucleophilic chiral phosphine 19i and subjected it to the aza MBH reaction of N sulfonyl imines with 2 cyclohexen 1 one or 2 cyclopenten 1 one [28]. The resulting adducts could be obtained in good yields, but with moderate enantiomeric excess (Scheme 13.16). 

This section of the volume concludes with procedures involving the elements Se, Ni, A1, Ti, and Rh. Paquette s method for dienophile activation via selenosulfonation is illustrated by the preparation of 1-(BEH2EHE-SULFONYL)CYCLOPENTENE, and the accompanying preparation of BICYCL0[4.3.03H0H-... 

Terminal epoxides react slowly with sulfonyl carbanions such as the homoenolate equivalent (1) (eq 4). With disubstituted epoxides and cyclic epoxides the reactions are slower still. For example, reaction of the lithio derivative of ethyl phenyl sulfone with cyclopentene oxide occurs in excellent yield (98%) after 10 h reflux in toluene. It has been reported that, in some cases, the addition of a Lewis acid (magnesium bromide, boron trifluoride etherate, 4 titanium tetraisopropoxide, MeOAl(i-Bu)2 ) or HMPA iirproves the yield dramatically. 

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