Mar. 30, 2006  6  US 2006/0069284 Al  [0095]  In this instance, b can be an optionally substituted  nitrogen and a and c can be oxygen, nitrogen or carbon, it  being possible for the two latter atoms to carry a hydrocar› bon radical or a hydrogen.  [0096]  For this type of reaction, reference is made to the  general work  Advanced Organic Chemistry,  third edition, by  Jerry March, page 743 et seq., and to the documents cited in  this reference work.  [0097]  The heating of these compounds gives cycloaddi› tion in the presence or absence of a solvent, even without  catalyst. However, some of the compounds with a canonical  form which has been mentioned above have to be synthe› sized in situ.  [0098]  The following nonlimiting examples illustrate the  invention.  [0099]  In this instance, Rfis trifluoromethyl, R$_{1 }$ and R$_{3 }$ are  hydrogen and  S  is chlorine.  [0102]  It was demonstrated that potassium carbonate  makes it possible to carry out this dehydrochlorination  reaction no longer at 25°  C. but at 60°  C. and in dipolar  aprotic solvents, such as DMF or NMP (DN=27.3):  [0100]  The reaction equation is given above with some of  the impurities identified.  (a) $^{19}$F NMR with internal standard;  (bladdition at 0° C. and then left to react at a.t.;  (c)addition at 0°  C., left in the ice bath for  ‰  hour and then left to react at a.t.;  (d)(16) and (21) could not be separated by $^{19}$F NMR: (16)  +  (21) - 12.3%  EXAMPLE 1  Dehydrohalogenation of the Precursor  CF $_{3}$CH$_{2}$CHClCH$_{2}$OAc  EXAMPLE 2  Dehydrohalogenation of the Precursor  CF$_{3}$ CH$_{2}$CHC1CH$_{2}$Oac in the Presence of DMF  EXAMPLE 3  Dehydrohalogenation of the Precursor  CF$_{3}$CH$_{2}$ CHC1CH$_{2}$ OAc Using Potassium Carbonate  [0101]  Base (leg),  temp (  /OAc  ~  K2C03,DMF  F3C  Cl  (2.)  /OAc DMF  ~  ~  DBU  F3C  OAc  F3C  Cl  (2)  (3)  Charges  RY (isolated) %  (2): 1830 g [8.95 mol]  DBU: 1500 g [9.85 mol]  DMF: 7.5 liters  25°  C., 2 to 3 hours  80%  Bases (pKa  of the  associated  (3a)  Base  t  Dc< 0 >  acid)  mmol  eq.  Solvents  (h) Temp. ( 0  c.)  (3a) %  DBU(12)  1.1  Diisopropyl ether  17  o(b) at a.t.  59  DN ~18  DBU(12)  1.1  Diisopropyl ether  4  50  69.2  DBU(12)  1.1  Diisopropyl ether  4  70  91  Et$_{3}$N (10.8)  1.1  Diisopropyl ether  17  20  14.5  Et$_{3}$N  1.1  Diisopropyl ether  4  50  5.8  DABCO  1.1  Diisopropyl ether  4  50  4.75  NaH (31)  2.44  0.9  PhCl  4  o(c) at a.t.  41.1  NaH (31)  0.98  0.9  THF (DN- 20)  4  o(c) at a.t.  67  KHMDZ (27)  1.8  0.6  THF  4  o(c) at a.t.  47.5  MeONa (15)  2.24  Diisopropyl ether  4  o(b) at a.t.  96  MeONa  2.80  0.8  Diisopropyl ether  4  o(b) at a.t.  84.8  MeONa  1.54  1.4 MeOH  4  o(c) at a.t.  100  RY<">  RY<">  RY<">  (16) %  (21) %  (22) %  CY%  0  49.1  0  83.22  0  71.2  0  102.89  0  77.5  0  85.16  0  0  0  0.00  0  0  0  0.00  0  traces  0  12.63  2.2  0  25.2  0.00  1.5  59.5  7.85  88.81  0  42  0  88.42  3.7  traces  23.3  2.60  n.d.(d)  n.d.(d)  56.8  n.d.  10.2  0  60.6  0.00 