Rautenstrauch rearrangements

A gold(m)-catalyzed Rautenstrauch rearrangement of the chromene 527 provides a chroman that features a 3,4-fused cycopentenone moiety 528, a reaction that is a viable alternative to Pauson-Khand type methodology (Equation 216) <2005JA5802>. 

Representative procedure for the gold-catalyzed Ohioff-Rautenstrauch rearrangement of 4-acetoxy-l-en-5-ynes. l-Phenylbicyclo[3.I.0]hexan-2-on ... 

A gold(I)-catalysed homo-Rautenstrauch rearrangement of 1-cyclopropyl propar-gylic esters to cyclohexenones is considered evidence for the gold-stabiUzed nonclassical carbocation character of intermediates. A mechanistic study revealed 0 partial chirality transfer from optically active propargyl acetates (Scheme 125). 

The Rautenstrauch rearrangement has been used in a number of total syntheses of polycyclic terpenoids. Fehr and Fiirstner have disclosed closely related approaches in the total synthesis of (-)-cubebol (Scheme 5.24), where the cycloisomerization of enantioenriched propargyl pivalates 66 occurs with good chirality transfer to give 67 in 77% yield [79-81]. Using similar strategies, various terpenoids derivatives have efficiently been obtained [80, 82]. 

Scheme 5.24 Total synthesis of (—)-cubebol featuring a Rautenstrauch rearrangement.

Finally, the use of nonterminal alkynes in Rautenstrauch rearrangements allows the construction of original polycyclic skeletons embedding a cyclopropane moiety through domino processes (Scheme 5.26) [86-88]. As a striking example, 70 stereoselectively yields the polycyclic fi amework 71 through a domino Rautenstrauch/Nazarov/cyclopropanation sequence. 

Faza ON, Lopez CS, Alvarez R, de Lera AR. Mechanism of the gold(l)-catalyzed Rautenstrauch rearrangement a center-to-helix-to-center chirality transfer. J. Am. Chem. Soc. 2006 128(7) 2434-2437. 

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