No abstract

A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in "green" solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific ipso-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B-C bond cleavage and facile protonolysis of a Au-σ-phenyl intermediate.

Radiopharmaceuticals that incorporate radioactive iodine in combination with single‐photon emission computed tomography imaging play a key role in nuclear medicine, with applications in drug development and disease diagnosis. Despite this importance, there are relatively few general methods for the incorporation of radioiodine into small molecules. This work reports a rapid air‐ and moisture‐stable ipso‐iododeboronation procedure that uses NIS in the non‐toxic, green solvent dimethyl carbonate. The fast reaction and mild conditions of the gold‐catalysed method led to the development of a highly efficient process for the radiolabelling of arenes, which constitutes the first example of an application of homogenous gold catalysis to selective radiosynthesis. This was exemplified by the efficient synthesis of radiolabelled meta‐[125I]iodobenzylguanidine, a radiopharmaceutical that is used for the imaging and therapy of human norepinephrine transporter‐expressing tumours.

Gold(I)‐catalysed intermolecular hydroalkoxylation of enantioenriched 1,3‐disubstituted allenes was previously reported to occur with poor chirality transfer due to rapid allene racemisation. The first intermolecular hydroalkoxylation of allenes with efficient chirality transfer is reported here, exploiting conditions that suppress allene racemisation. A full substrate scope study reveals that excellent regio‐ and stereoselectivities are achieved when a σ‐withdrawing substituent is present.

Intermolecular additions of thiols to allenols via formal S(N)2' selectivity to produce functionalized dienes are described. Although this dehydrative reaction was initially developed using gold(I) catalysis, indium(III) proves to be a far superior catalyst in terms of selectivity and substrate scope.

Indium(III) chloride can be used as a cheaper alternative to gold(I) complexes as a catalyst in dehydrative reactions with allylic alcohols. There is often an improvement in yield and, in particular, indium(III) chloride outperforms gold(I) as a catalyst in chemoselective reactions. For example, substrates with pendent alkyne or alkene groups react poorly under gold(I) catalysis, but are better tolerated under indium(III) chloride catalysis.

Gold-Catalyzed Proto-and Deuterodeboronation. -A Au(I)-catalyzed protodeboration of a variety of arylboronic acids using dimethylcarbonate as the solvent is presented. In the presence of D 2O the corresponding regioselectively deuterated products are obtained. -(BARKER, G.; WEBSTER, S.; JOHNSON, D. G.; CURLEY, R.; ANDREWS, M.; YOUNG, P. C.; MACGREGOR*, S. A.; LEE, A.-L.; J. Org. Chem. 80 (2015) 20, 9807-9816, http://dx.doi.org/10.1021/acs.joc.5b01041 ; Inst. Chem. Sci., Heriot-Watt Univ., Riccarton, Edinburgh EH14 4AS, UK; Eng.) -Mais 10-026

A formal SN2′ addition of thiols to allenols is developed.