Rhodium 2,3 -sigmatropic

The [3,3]-sigmatropic rearrangement ofpropargyl esters [234, 561] is usually an equilibrium reaction for example steric repulsion can help to deliver mainly the allene [562] and faster reaction kinetics are observed with silver(I) and copper(I) catalysts [562-571] (see cyclopropane 169 in Scheme 1.75) [572], and recently also rhodium(I) catalysts [573]. 

Several new chiral rhodium(II) catalysts have been synthesized for evaluation as catalysts in the asymmetric oxonium ylide-[2,3]-sigmatropic rearrangements of diazocarbonyl substrates219 (see Scheme 46). The formation of 13-membered ring oxonium ylides (165) and their stereo-controlled [2,3]-sigmatropic rearrangement to 10-membered ring lactones (166) have been described.220... 

The [3+2] cycloreversion of bicyclo[ z.3.0]alkan-3-on-2-yl-l-oxonium ylides (m = 3-6) to alkenyloxyketenes is observed and extensively studied <2004JOC1331>. In particular, rhodium(ll)-catalyzed intramolecular reaction of diazomethyl oxepan-2-yl ketone 13 generates a bicyclo[5.3.0]decan-3-one-l-oxonium-2-ylide 14, which undergoes sigmatropic and stereospecific [3+2] cycloreversion to form hept-6-enyloxyketene 15. The latter is trapped by MeOH to form the corresponding ester 16 (Scheme 5). 

The [2,3]sigmatropic rearrangement of sulfonium ylide (24) derived from rhodium-catalyzed decomposition of ethyl 3,3,3-trifluoro-2-diazopropanoate (23) in the presence of propargyl sulfide (22a) affords the corresponding functionalized CF3-containing carboxylic ester sulfide (25a). The latter was... 

Schemes [2,3]Sigmatropic rearrangement of sulfonium ylides via rhodium-catalyzed decomposition of ethyl 3,3,3-trifluoro-2-diazopropionate...

Compounds 116 originated from a 2,3-sigmatropic rearrangement of the oxygen ylide 118, while compounds 117 are formed by a 1,2-insertion reaction. No cyclopropanation took place with analogous thioacetals. The carboxylate counter-ion in the rhodium(II)... 

Tandem intramolecular ylide formation and [2,3]-sigmatropic rearrangement from copper carbenoids is a useful method for preparing seven- and eight-membered cyclic amines 68 (n = 3, R = Me = 4, R = C-C3H5). The rhodium(II) acetate-catalyzed reaction is less effective (94CC2701). 

Recently, the known method for the synthesis of thiolanes by cyclization of diazo ketosulfides (72CC860) has received further development (92TL169 95JOC53). It was found that sulfur-containing a-diazo ketones 437 bearing a tethered alkyne unit decomposed in the presence of Rh2(OAc)4 via the addition of the rhodium-stabilized carbenoid onto the acetylene jr-bond to give a vinyl carbenoid, followed by sulfonium ylide formation and a subsequent [2,3]- or [l,2]-sigmatropic shift. This transfor-... 

The rhodium(II) acetate-catalyzed reaction of ethyl diazoacetate with 1,3-dithiolane 640 (n = 1 R = Me), via a [2,3]-sigmatropic rearrange-... 

Vedejs has iso discussed the inefficiency of copper catalysts in ylidic 3,2-sigmatropic processes. Optimization of ring expansion reactions using diazomalonates were found to be unsatisfactory and analogous reactions using diazoketones were totally unsuccessful. Takano has taken advantage of a rhodium-promoted ylide formation followed by a 3,2-rearrangement, in a useful synthesis of y,8-unsaturated carbonyl compounds (Scheme 45). ... 

A modification called tandem [2,3] sigmatropic rearrangement of sulfonium ylide—bromine allylic rearrangement has been reported (88JOC5149). Thus, reaction of the C5 brominated 2-pyrone 224 with ethyl diazoacetate under rhodium catalysis results not only in transfer of the ester moiety to C5, as described earlier, but also in the transfer of the bromine atom from C5 to the side chain at C6 in such a way that the functional group remaining at that side chain, as in 225, can be further elaborated (89JHC1205). 

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