Crabbe reaction

The lactam 145, bearing a terminal triple bond, is transformed into the corresponding allene derivative 146 through a Crabbe reaction (Equation 7). Using Pd(PPh ()4 as the catalyst and in the presence of phenyl iodide, the corresponding indolizine is obtained. The lactam nitrogen atom is added to the central carbon atom of the allene... 

When propargylamine 183 was subjected to a homologative allenylation (Crabbe reaction) at 100 °C, the resulting allene underwent a spontaneous Diels-Alder reaction to give the adduct 184. This intramolecular cycloaddition-oxidation sequence provided a simple route to indole alkaloids such as hippadine and ds-trikentrin B [148]. 

In addition to a-allenic a-amino acids, the corresponding allenic derivatives of y-aminobutyric acid (GABA) have also been synthesized as potential inhibitors of the pyridoxal phosphate-dependent enzyme GABA-aminotransferase (Scheme 18.49) [131,138-142]. The synthesis of y-allenyl-GABA (152) and its methylated derivatives was accomplished through Crabbe reaction [131], aza-Cope rearrangement [138] and lactam allenylation [139], whereas the fluoroallene 153 was prepared by SN2 -reduc-tion of a propargylic chloride [141]. 

Pyrroles can be synthesized from 3-pyrrolines 39 which can be prepared from a Crabbe reaction of propargyl sulfonamides 38 and selective cycloisomerization of the resulting allene intermediate. Subsequent oxidation of 3-pyrrohnes with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) lead to 2-alkyl and aryl pyrroles 40 in this domino process (14EJO2305). 

One of the most popular methods for the synthesis of allenes is the Sn2 reaction of propargylic derivatives with organocopper reagents [1, 2], Most probably a study published in 1968-69 by Rona and Crabbe represents the first example of the Cu(I)-mediated SN2 reaction of propargylic electrophiles giving allenic products (Scheme 3.32) [69, 70], Since then, many researchers have used modified organocopper reagents with stoichiometric or catalytic amounts of Cu(I) salt. 

In a similar manner Crabb and Schofield852 have described 11n lactonisathm effect in the per benzoic add epaxidation of certain substituted benzocycloheptone derivatives, and Howell and Taylor - did so for the reaction of an indeno, ae shown in Eq . (46) and (47). 

Barkworth, P. M. R. and Crabb, T. A.. Compounds with bridgehead nitrogen. XLlll. The reaction between trans-2-amin[Pg.75]

Dehydration. Burgess et al. reported that the reagent is useful for dehydration of simple alcohols. The reaction is a stereospecific ds elimination and follows Saytzeflf s rule. Crabbe and Leon have used this procedure with various steroidal secondary and tertiary alcohols. They conclude that the nature of the alcohol group, the configuration, and the environment are the primary factors governing the course of dehydration. The reactions are carried out at room temperature in anhydrous benzene for 2 hr. followed... 

The preparative procedure for prochiral triketone 34 was simplified a solution of 34 and unnatural D-(+)-proline in dimethyl sulfoxide was degassed and then stirred at room temperature for 6 days, although Crabbe and coworkers reported a time saving variation of the preparation by using DMF as solvent.24 The reaction mixture was worked up, and the crude product obtained was purified by a vacuum distillation and by a column chromatography on silica gel to give optically active (8af )-(-)-33, [a]o -68.4° (c 1.355, benzene) as a syrup in 82% chemical and 69% optical yields. 

A very interesting finding can perhaps modify the vision we have presently of the reaction. In the case of the homogeneous reaction, we found that a partial pressure of water in the feed promotes propane conversion. Fig. 10 shows the dramatic difference [98]. This makes the performance of the homogeneous reaction at a given temperature very close to those of the catalysed reaction at this temperature. An interesting observation is that the production of byproduct ethylene is very little affected by conversion and almost not at all by the presence of water [98]. Fig. 11 gives propene selectivity as a function of propane conversion [98]. This seems to exceed the performances indicated by Burch and Crabb. It is not yet known whether similar effects could take place in catalysed reactions. 

An even simpler protocol is employed in the formation of A-phenylthiocar-bamoyl derivatives (PTC-amino acids, C6H5NHCSNHCHRC02H Figure 4.1) by reaction in a suitable buffer with the Edman reagent, phenyl isothiocyanate (West and Crabb, 1989). 

P MacLaurin, NC Crabb, I Wells, PJ Worsfold, D Coombs. Quantitative in situ monitoring of an elevated temperature reaction using a water-cooled mid-infrared fiber-optic probe. Anal Chem 68 1116-1123, 1996. 

MACDOUGALL, D. B. and GRANOR, M. (1998). Relationship between ultraviolet and visible spectra, in O Brien, E., Nursten, H. E., Crabbe, M. J. C. and Ames, J. A. (eds) The Maillard Reaction in Foods and Medicine, The Royal Society of Chemistry. Special publication 223, Cambridge, pp. 160-165. 

Blank I, Devaud S. and Fay L.B. (1998) Study on the formation and decomposition of the Amadori compound N-(l-deoxy-D-fructos-l-yl)-glycine in Maillard model systems. 6th Int. Symp. Maillard react., The Maillard reaction in foods and medicine, J.O Brien, H.E. Nursten, J.C. Crabbe, J.M. Ames, Eds, Royal Society of Chemistry, London, 43-50. 

Tressl R, Kersten E., Wondrak G., Rewicki D. and Kruger R.P, (1998d) Fragmentation of sugar skeletons and formation of Maillard polymers. 6th Int, Symp. on Maillard react., The Maillard Reaction in Foods and Medicine, O Brien J, Nursten H.E., Crabbe J.C, and Ames J.M. Eds, Royal Society of Chemistry, London, pp. 69-75,... 

Reaction in Foods and Medicine O Brien J., Nursten H.E., Crabbe J.C. and Ames J.M., Eds. Royal Society of Chemistry, London. 

Crabbe, M.J., Cataract as a conformational disease - the Maillard reaction, alpha-crystallin and chemotherapy. Cell Mol Biol 44 (1998) 1047-1050. 

Reaction with aldehydes. Crabbe et a/. report that dimethylcopperlithium (2 eq.) usually reacts with aldehydes to give products of 1,2-addition sometimes the primary alcohol is also formed by a reductive process. 

Carbomethoxysulfamoyltriethylammonium hydroxide inner salt added to a soln. of ll/ -hydroxy-17 20, 20 21-bismethylenedioxypregn 4-ene-3-one in anhydrous benzene, and stirred 2 hrs. at room temp. 17 20,20 21-bismethylenedioxy-pregna-4,9(ll)-diene-3-one. Y 96%. - The 1 la-isomer gives only 9% yield. The mild conditions and selectivity of the reaction as well as the unexpected nature of some products make this method attractive for the introduction of double bonds into steroids. F. e. s. P. Crabbe and C. Leon, J. Org. Chem. 55, 2594 (1970). 

A simple conversion of 11-deoxy-PGE2 into PGA2 through reaction of the silyl enol-ether (70) with Pb(OAc) and subsequent desilylation has been described by Crabbe. ... 

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