AUylic transposition

Allylboranes, which are available from organometallics or l droboration, undergo oxidation without aUylic transposition and with retention of stoeochemistry. This qrplies both to regio- and stereo-chemically deHned allylic dialkylboryP and allylic dialkoxyb P compounds (equations 14 and IS). 

AUylic transpositions. Ally lie alcohols undergo 1,3-transposition at room... 

Overman, L.E. and Zipp, G.G. 1997. AUyhc transposition of alcohol and amine functionality by thermal or palladium (ll)-catalyzed rearrangements of aUylic A-benzoylbenzimidates. Journal of Organic Chemistry, 62 2288-91. 

A similar transposition can be applied to saturated ketones. For example, a ketone is treated with a vinyl organometallic reagent to generate a derivative of an aUylic alcohol. Reaction with benzenesulfenyl chloride then gives an aUylic sulfoxide by means of a [2,3] sigmatropic rearrangement. The remain-... 

The epimeric (+)-a-allokainic acid was constructed by the unsaturated imide/ alkyne alkylative coupling of 9 with trimethylaluminum in 73% yield and 97 3 diastereoselectivity (Scheme 8.11) [33]. This was followed by silyl to carbonate protecting group transposition, stereoselective aUylic reduction, and removal of protecting groups to afford (+)-a-allokainic acid. The complementary nature of these two stereodivergent approaches allowed access to both epimeric natural products. 

Reductive Transposition of Allylic Alcohols. In direct anal ogy to the synthesis of allenes from propargylie alcohols, invertlve (Mitsunobu) displacement of aUylic alcohols with NBSH fol lowed by warming of the reaction mixture to ambient temperature to Induce diazene formation and sigmatropic loss of dinitrogen provides reductively transposed alkenes. This methodology has proven to be highly effective for the reductive 1,3 transposition of a wide variety of allylic alcohols (eq 3). ... 

AUylic thiocarbamates are known to undergo an O—migration under a variety of conditions A comparison of the individual methods reveals that thermally induced and Pd(II)-catalyzed rearranganents proceed mainly as [3,3] sigmatropic shifts, whereas Pd(0) catalysis exhibits features typical of the involvement of (i7 -allyl)Pd intermediates (Scheme 7). Thus, while 5 gives mainly the transposition product 7 on heating or in the presence of Pd(II), the Pd(0)-catalyzed reaction shows a preference for the characteristic attack by the nucleophile on the less substituted carbon (6). Furthermore, partial loss of diastereopurity has been observed for the thermal and Pd(ll)-catalyzed reaction of the carveyl derivative 8, whereas the Pd(0)-catalyzed reaction was stereospedlicJ ... 

The only synthetic apfdicadon of an aUylic S S transposition (equation 25) seems to be in the synthesis of ( ) a, -unsan]lated aldehydes via a 3.3-signiatnq>ic leanangement of allylic didiiocarbamates (Scheme 35). ... 

Carbopalladation of dienes yields 7r-allylpalladium intennediates capable of capturing nucleophiles. An example of this type of reaction in natural product synthesis is the conversion of the aryl iodide 168 into pentacycle 169. After 6-exo carbopalladation the free phenol is captured by the resultant Tr-allylpaUadium intermediate to yield aUyUc ether 169 en route to (-)-morphine 120. The domino reaction closes a srx-membered ring, forges a quaternary center, and forms a five-membered furan ring. The reaction sequence has also been effectively reversed in a construction of (+)-y-lycorane 172. Treatment of aUylic benzoate 170 with a palladium catalyst in the presence of sodium hydride triggers tt-allylpalladium formation and intramolecular amide capture. rr-Allylpalladium formation occurs with inversion, as does reaction with the pendant amide, resulting in a net retentive 1,3-transposition of stereochemical information. Subsequent addition of base and thermolysis induces 6-exo intramolecular carbopalladation to yield alkene 171. 

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