Transposition, oxygen

The transposition of oxygen in allylic esters (R6 = alkyl, phenyl) or carbamates [R6 = N(CH3)2] has the same overall bonding changes as the thermal [3,3] sigmatropic Claisen or Cope rearrangements. Chirality transfer from C-l to C-3 is accompanied by 1,3 oxygen transposition (carbonyl O to allylic O ). 

The [3,3]-sigmatropic rearrangement of allylic acetates, catalysed by soluble Pd salts, that was reported last year (4,152) as a method for [1,3]-oxygen transposition has recently been shown to occur suprafacially with complete chirality transfer an example is the conversion (70) (71). Overman has... 

Subsequent hydride shift-mediated oxygen transposition should then generate 370. The furanophane 367 in turn, featuring a trisubstituted double bond with ( )-configuration (necessary for the success of the TADA reaction), was to be generated by RCM. 

The rearrangement of the allylic acetate in the prostaglandin side chain (entries 3 and 4) demonstrates the influence of chirality and double-bond geometryl8- 24-25-39. Oxygen transposition in the (Z)-allylic acetate led to the (15.S (-acetate with the E configuration of the new double bond, whereas the ( )-acetate gave under similar conditions the (15R)-acetate, also with the E configuration of the double bond. 

Synthetic utility of the Wharton reaction in alkaloids can be exemplified by the oxygen transposition of epoxyketone 28 to allylic alcohol 29.14 Many similar cases have been reported.15 16... 

Advantage was taken of the Wharton reaction to carry out an oxygen transposition of 32 to provide 33, which was only two steps away from 11-deoxy-prostaglandin Fi0 after de-silylation and hydrolysis.18... 

The allylic hydroperoxides generated by singlet oxygen oxidation are normally reduced to the corresponding allylic alcohol. The net synthetic transformation is then formation of an allylic alcohol with transposition of the double bond. 

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