Marzia Mazzacurati

The First Flights of a Molecular Shuttle Transporting Elements: Easy One‐pot Formation of Organic Cyclic Arsanes, Stibanes and Bismutanes

The increasing role of organic derivatives of arsenic, antimony, and bismuth in many fields of chemistry is due to their versatility as ligands, their use in materials science and their applications in the pharmacological field. Despite this, few methods of synthesis of triorganoderivatives of these elements have been reported to date and they all involve multi-step procedures giving products in very low overall yields. Moreover, the toxicity of these derivatives requires that their preparation must be carried out with strong attention and adequate precautions in their handling. For these reasons, to find synthetic one-pot procedures that permit the manipulation of these compounds to be minimised represents an interesting challenge. Here we report a very simple synthesis of new arsenic-, antimonyand bismuth-donor reagents and their use in the one-pot synthesis of cyclic arsanes, stibanes and bismutanes, respectively, through a procedure in which the simultaneous formation of three C As, C Sb or C Bi bonds is achieved. Recently, we reported (Scheme 1) a new synthesis of tertiary cyclic phosphanes 2 and 3 in 60–70 % yields by addition of a bis ACHTUNGTRENNUNG(Grignard) reagent and a Grignard reagent to an unusual phosphorus-donor reagent, the benzothiadiphosphole 1 a, called by us a “butterfly reagent” owing to its particular folded structure. At the end of the reaction the starting reagent 1 a was quantitatively regenerated by addition of one equivalent amount of PCl3 to the end-product 4, which is the remainder of 1 a obtained after quenching the reaction mixture with water (Scheme 1). More recently, we found that tertiary phosphanes are formed spontaneously in the reaction mixture, and that the quantitative regeneration of the reagent 1 a can be accomplished by simple addition of one equivalent amount of PCl3 to the crude reaction mixture. Taking these findings into consideration, together with the fact that as As, Sb and Bi, belong to the same group of P they could show similar behaviour, we decided to try a transport process for these elements, in order to find a new protocol for obtaining cyclic organoarsanes, organostibanes and organobismutanes, which, to date, have been synthesised with multi-step procedures and in very low overall yields. For this purpose, firstly we tried the synthesis of new heterocycles 1 b–d (Scheme 2), by reaction between compound 4 and AsCl3, SbCl3, and BiCl3, respectively. [10] With this reaction benzothiaphospharsole (1 b), benzothiaphosphastibole (1 c), and benzothiaphosphabismole (1 d ; Scheme 2) were isolated in almost quantitative yields (95–98 %) and characterised. It is worth noting that mass spectra of 1 a–d showed the same peak (m/z= 243), originating by the loss from the molecular ion of the fragment PS, AsS, SbS and BiS, respectively. At the same time, the P NMR spectra showed a regular decrease of the chemical shifts on going from 1 b (d= 78.6 ppm) to 1 c (d= 52.7 ppm), to 1 d (d=35.0 ppm) in [D8]THF, as a result both of the decrease in electronegativi[a] Prof. G. Baccolini, Dr. C. Boga, Dr. M. Mazzacurati, Dr. G. Micheletti Department of Organic Chemistry “A. Mangini” ALMA MATER STUDIORUM—Universit di Bologna Viale Risorgimento, 4 40136 Bologna (Italy) Fax: (+39) 051 2093654 E-mail : baccolin@ms.fci.unibo.it boga@ms.fci.unibo.it Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200802007. Scheme 1. One-pot synthesis of tertiary phosphanes.