By Enolate Trapping

Addition of BuiSnLi to cyclohex-2-enone followed by enolate trapping with n-decyl iodide proceeded with high diastereoselectivity to provide the 2,3-rrdiR5-stannyl ketone (16), which could be equilibrated with the cis diastereomer (17) upon treatment with base. LAH reduction, followed by separation of the diasteteomers, afforded samples of the 2-alkyl-3-stannylcyclohexanols as shown in Scheme 17. Iodine(III)-mediated fragmentation was shown to proceed in a stereospecific anti manner, with either of the rrdiRr-2,3-cyclohexanols affording ( )-enal (18), and the cir-2,3-alcohol the (Z)-enal (19 Scheme 17). Enal (18) was then utilized in a stereoselective synthesis of the mosquito pheromone, erythro-6-asx-toxyhexadiecan-S-olide (20 Scheme 18). ... 

Danishefsky and his co-workers have also achieved a total synthesis of quadrone (103), another interesting synthetic target containing annulated cyclopentane rings. Conjugate addition, followed by enolate trapping served to convert (99) to (100). Further elaboration including Aldol cyclization yielded the key intermediate (101), which underwent base-induced cyclization to (102), which in turn was converted to ( )-quadrone (103). 

The reduction rate of R (low reduction potential)1 is faster than any chemical reaction such as trapping by enolate ion. The difference from the electrochemical results is that, in the latter, the secondary reduction of the sulfinate anion does not occur. 

C. Regioselective silylation of ketones by in situ enolate trapping... 

The sequence of chiral 1,4-reduction of a fi-substituted cyclopentenone followed by electrophilic trapping of the intermediate enolate provides an efficient route to chiral 2,3-disubstituted cyclopentanones that generates two chiral centers in the process (Eq. 352)459... 

Scheme 2.28 Functionalized allenes obtained by 1,6-cuprate addition to acceptor-substituted enynes and regioselective enolate trapping with methyl triflate (77), aldehydes (78, 79), ketones (80) and silyl halides (81).

In analogy with reactions discussed with the examples of Schemes 6.12 and 6.13, 74 and 82 were trapped by enolates. Without exception, the enolate /3-carbon atom attacked the central carbon atom of the allene moiety with eventual formation of 3-methylenecyclobutanol derivatives as major products in most cases [64, 77]. This type of reaction is illustrated in Scheme 6.23 by two examples. 

It has been demonstrated35 that enolate trapping by the electrophilic iron-carbene complex 1 provides 2. Alkylation at sulfur followed by a-elimination again generates a carbene, which then inserts stoichiometrically 1,5 into the C —H bond to give the octahydroindenone 3. Several other applications of this cyclization have been published 3fi. 

The transformations of 1-iodo-1,4-dienes and 1,5-dienes are generally similar to the reactions of < -iodoalkenyl-benzenes. In the absence of external nucleophile, palladium hydride abstraction or intramolecular trapping by enolate take place (Scheme 11)/ ... 

Intramolecular carbonylative cross-coupling involving enolizable GH-acidic fragments has been described by Negishi et al. In this case, trapping of acylpalladium intermediate is effected formally by enolate, either with carbon or oxygen center (Scheme 28). 

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