Overman rearrangement of allylic

Stereoselective rearrangement reactions can involve sugar-linked functionalities. An example of this type is the Overman rearrangement of allylic trichloracetimidates formed from a D-glucofuranose derivative 20 [36]. This methods affords (L)-a-ami-no acids 25 from (Z)-allylic imidate 23 and (R)-a-amino acids 25 from ( )-imidates 23 with a diastereoselectivity of about 16 1. The oxidative cleavage of compound 24 with Ru04 yields the a-amino acid 25, (Scheme 15). 

The total synthesis of (-l-)-lactacystin (1) has been achieved via Overman rearrangement of allylic trichloroacetimidate derived from D-glucose as an effective method for chiral synthesis of a,a-disubstituted amino acid derivatives (Schemes 1 and Selective... 

As a preliminary mechanistic proposal, we hypothesize that the palladimn(ll)-phosphoramidite catalyst acts as a chiral n-acid to activate the amine iV-oxide substrate (Scheme 1S.291. similar to the mechanism proposed for the Overman rearrangement of allylic trichloroacetimidates. While it is not clear whether the reactive species is oxide-bound complex 119a or olefin-bound complex 119b, we propose heterocycle 120 as an intermediate in this cyclization-induced mechanism Grob-type fragmentation eventually reveals O-allylhydroxylamine 117 and the palladium(n)-phosphoramidite catalyst, which can reenter the catalytic cycle. 

Yang has shown that the Overman rearrangement of allylic tri-chloroacetimidates to allylic trichloroacetamides can be efficiently catalysed by gold(i) chloride in water (Scheme 16.31). The rearrangement worked well under mild conditions (55 °C), and in short reaction times (2-6 h). The reaction work up appeared to be very simple as the final product was cleanly obtained by simple extraction. The authors were able to conduct the reaction on a gram scale using 2 mol% of the gold catalyst. 

Caller M, Hollis TK, Overman LE, Ziller J, Zipp GG (1997) First enantioselective catalyst for the rearrangement of allylic imidates to allylic amides. J Org Chem 62 1449-1456... 

Donde Y, Overman LE (1999) High enantioselection in the rearrangement of allylic imidates with ferrocenyl oxazoline catalysts. J Am Chem Soc 121 2933-2934... 

Overman LE, Owen CE, Pavan MM, Richards CJ (2003) Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines. Org Lett 5 1809-1812... 

Anderson CE, Overman LE (2003) Catalytic asymmetric rearrangement of allylic trichlor-oacetimidates. A practical method for preparing allylic amines and congeners of high enantiomeric purity. J Am Chem Soc 125 12412-12413... 

The synthesis started with levoglucosenone 4, available by the pyrolysis of cellulose, e.g. old newspapers. Bromination-dehydrobromination gave the enantiomerically-pure Diels-Alder dienophile 5, which was combined with isoprene to give predominantly the crystalline adduct 1. Hydrolysis and acetylation led to 6, which was carried on to the geometrically-defined allylic alcohol 7 via reduction with Zn-Cu couple. Overman rearrangement of 7 proceeded with high facial control, to give 8. 

In a complementary approach, Larry Overman of the University of California at Irvine, has developed (J. Org. Chem. 2004,69,8101) a Co catalyst that effects the rearrangement of allylic imidates such as 9 with high . There is no need for the starting allylic alcohols to be perfectly trans, as imidates from cis allylic alcohols do not participate in the rearrangement. 

Larry E. Overman and Gilbert M. Rishton 63 STEREOCONTROLLED PREPARATION OF 3-ACYLTETRAHYDROFURANS FROM ACID-PROMOTED REARRANGEMENTS OF ALLYLIC KETALS (2S,3S)-3-ACETYL-8-CARBOETHOXY-2.3-DIMETHYL-1-OXA-8-AZASPIRO[4.5]DECANE... 

Overman, L. E. Zipp, G. G. Allylic transposition of alcohol and amine functionality by thermal or Pd(II)-catalyzed rearrangements of allylic N-benzoylbenzimidates. J. Org. Chem. 1997, 62, 2288-2291. 

The Overman rearrangement, a thermal [3,3]-sigmatropic rearrangement of allylic trichloroacetimidates, is an attractive procedure for the preparation of ally] amines from allyl alcohols (Eq. (4)) [7]. 

L. E. Overman, Thermal and mercuric ion catalyzed [3,3]-sigmatropic rearrangement of allylic trichloroacetimidates. 1,3-Transposition of alcohol and amine functions,. /. Am. Chem. Soc., 96 (1974) 597-599. 

Rearrangement of Allylic Imidates. Overman and co-workers reported an interesting application of this chiral diamine to induce enantioselectivity in Pd(II)-catalyzed rearrangement of allylic imidates to allylic amides (eq 5). 

The rearrangement of allyl trichloroacetimidate into allyl trichloroacetamide (Overman rearrangement) has been used for the synthesis of amino sugars. For example, the trichloroace-... 

In the recent total synthesis of sphingofungin E (90), Overman rearrangement of an allylic trichloroacetimidate derived from diacetone-D-glucose 91 generated tetra-substituted carbon... 

Donde, Y., Overman, L. E. High Enantioselection in the Rearrangement of Allylic Imidates with Ferrocenyl Oxazoline Catalysts. J. Am. Chem. Soc. 1999, 121, 2933-2934. 

Overman, L. E., Campbell, C. B. Mercury(ll)-catalyzed 3,3-sigmatropic rearrangements of allylic N,N-dimethylcarbamates. A mild method for allylic equilibrations and contrathermodynamic allylic isomer enrichments. J. Org. Chem. 1976, 41, 3338-3340. 

The hetero-Cope rearrangement of allylic iminoesters, established by Overman for non fluorinated molecules (2d), leads to formal S -substitution of an hydroxy group by a nitrogen functionality. 

The catalysed rearrangement of allylic imidates including allylic trichloroace-timidates such as (12.12) has been reported by Overman using palladium catalysts with some of the highest ees obtained using the cobalt oxazoline palladacycle (12.13). 

Overman and co-workers carried out extensive studies on Pd(II)-catalyzed asymmetric allylic rearrangement of allylic imidates to form enantioenriched allylic amides. They achieved 97 % ee as the best result by the reaction of the allylic imidate 612 using the cyclopalladated ferrocenyl oxazoline 613 having elements of planar chirality as a catalyst precursor, and discussed the mechanism of the reaction [220]. 

In some cases, the mercury(II)- and palladium(II)-catalysed allylic Overman rearrangement of trichloroacetimidates can be accomplished under mild conditions at room temperature or even much lower temperature. For example, the trichloroacetimidic ester of geraniol 12 is converted to linalyl trichloroacetamide 13 when treated with 0.2 equiv of mercuric trifluoroacetate at room temperature for 10 min. This catalytic... 

Since its discovery in 1974, more than 180 papers have been published on the use of the Overmann rearrangement to prepare allylic amines and their analogs from their allylic alcohols. For example, a recent synthesis of the fluoroalkene peptidomimetic precursor of A -acetyl-Z,-glutamyI-Z.-alanine involves the Overman rearrangement of the imidate derived from the allylic alcohol 60. ° This alcohol is readily prepared through Evans asymmetric aldol reaction of oxozolidinone with an aldehyde. 

The Overman rearrangement of the disubstituted allylic trichloroace-timidates has also been used in the construction of trisubstituted carbons bearing a nitrogen substituent. For instance, heating a solution of the imidate 71 in refluxing xylene fiimishes the allylic trichloroacetamide 72 in good yield. Compound 72 is a precursor to aminocyclopentanol Ti ... 

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