Department of Chemistry, UniVersity of LeuVen,Celestijnenlaan 200F, B-3001 LeuVen, Belgium, NationalInstitute of AdVanced Industrial Science and Technology,AIST Tsukuba Central 5, Tsukuba 305-8565, Japan, andDepartment of Information Systems Engineering, Faculty ofEngineering, Osaka Sangyo UniVersity, Daito 574, JapanReceiVed: January 23, 2001; In Final Form: July 5, 2001In this note, we comment on the electronic mechanism ofthe concerted 1,3-dipolar cycloaddition reaction of fulminic acidto acetylene (HCNO + HCCH), which has recently been studiedby valence bond and molecular orbital approaches by fourdifferent groups including ourselves: (i) Sakata, K. J. Phys.Chem. A 2000, 104, 10001, (ii) Harcourt, R. D.; Schulz, A. J.Phys. Chem. A 2000, 104, 6510, (iii) Nguyen, M. T.; Chandra,A. K.; Sakai, S.; Morokuma, K. J. Org. Chem. 1999, 64, 65,and (iv) Karadakov, P. B.; Cooper, D. L.; Gerratt, J. Theor.Chem. Acc. 1998, 100, 222. The main discrepancy arising fromthese theoretical studies concerns the electronic reorganization,and in particular, the direction of the electron flow accompany-ing the nuclear deformation at the transition structure. Wepresent additional results supporting our earlier findings that inthe 1,3-dipolar cycloaddition of fulminic acid (HCNO) andprobably substituted nitrile-oxides (RCNO), to alkynes andphosphaalkynes, the oxygen (O) atom behaves as a bondacceptor center and the carbon (C) as a bond donor.The 1,3-dipolar cycloaddition is a general and powerfulmethod for the synthesis of five-membered heterocyclic com-pounds owing to the great variety and availability of dipolesand dipolarophiles.
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