Furo pyridazines

H-Furo[3,4-e]pyrazole, 1,4-dihydro-4-oxo-l-substituted synthesis, 6, 989 Furo[2,3-d]pyrazoles synthesis, 6, 998 Furo[3,4-d]pyrazoles synthesis, 6, 998 Furo[2,3-d]pyridazine H NMR, 4, 984 synthesis, 4, 984... 

Furo[2,3-d]pyridazine, 7-hydrazino-synthesis, 4, 985 Furo[3,4-d]pyridazine synthesis, 4, 985... 

Furo[3,4-d]pyridazine-1,4-diones synthesis, 4, 985 Furopyridazines, 4, 984 Furo[2,3-6]pyridine, 3-amino-synthesis, 4, 977 Furo[2,3-6]pyridine, 4-methyl-synthesis, 4, 976 Furo[2,3-6]pyridine, 6-methyl-synthesis, 4, 976 Furo[2,3-6]pyridine, 5-nitro-synthesis, 4, 977 Furo[3,2-c]pyridine, 4-allyl-synthesis, 4, 982 Furopyri dines H NMR, 4, 983 physical data, 4, 983 properties, 4, 982 synthesis, 4, 974-982 UV spectroscopy, 4, 983 Furo[6]pyri dines HMO data, 4, 975 Furo[2,3-6]pyri dines synthesis, 4, 974-977 7, 512 Furo[3,2-6]pyri dines C NMR, 4, 982 synthesis, 4, 648, 981 Furo[c]pyri dines HMO data, 4, 976 Furo[2,3-c]pyri dines synthesis, 4, 977 Furo[3,2-c]pyri dines nitration, 4, 983 synthesis, 4, 978-981 Furo[3,4-c]pyri dines synthesis, 4, 982 Furo[3,2-c]pyridin-3-ols synthesis, 4, 980 Furo[2,3-6]pyridin-6-ones synthesis, 4, 976 Furo[3,4-c]pyridin-4-ones synthesis, 4, 982... 

Other fused pyridazines, i.e. furo- and benzo-fused derivatives, sometimes also partly give the corresponding 1,2-diazocine systems.910... 

N pyrrolo[3,4-d]pyridazine O furo[3,4-d]pyridazine S thieno[3,4-d]pyridazine... 

The formation of pyrrolo-, furo-, and thieno[2,3- pyridazines has been predicted on the basis of thermodynamic studies <2005JOC998>. 

Apart from a very unconventional synthesis of 274 via fragmentation of the tetrazine 273 in the presence of furan (Equation 97) <2003AJC811>, interest in the furo[3,4-r/ pyridazines has waned since the coverage in CHEC-II(1996) <1996CHEC-II(7)229>. 

Only two examples of an aromatic species of this isomer of fused pyridazine have been reported. The furo[3,2-f]-pyridazine, 276, has been prepared in modest yield from the pyridazine 275 upon treatment with carboalkoxymethyl-triphenylphosphoranes (Equation 98) <2004PS(179)97>. The structure was confirmed by spectroscopic evidence and results by rearrangement of an intermediate alkylidene structure. 

A series of 3-chloro-4-arylacetylenic pyridazines have been cyclized to the corresponding 5-aryl-furo(or pyrrolo or thia)[2,3-( ]pyridazinones <2006TL6125, 2006JMC3753>. 

Introduction of nitrogen atoms into both positions 5 and 6 in 4 enhances the stability of the system tremendously. Furo[3,4-d]pyridazine (330) is available from 329 (Eq. 15) as yellowish crystals (mp 161 C) which can be sublimed at 145 C/0.1 torr. . A further number of furo[3,4-J]pyridazines... 

Furo[3,4-J]pyridazines have also been used in Diels-Alder reactions (331a with maleic anhydride, acrylic acid, 1,4-naphthoquinone, dibenzoyl-ethylene, 1,4-benzoquinone, benzo[c]furandione ° 331c with maleic anhydride) 331a has been shown to be more reactive than 331c. 1,3-Diphenylfuro[3,4-b]quinoxaline (335) has been obtained from phthalide 334 (Eq. 17) as a green crystalline, quite stable solid (mp 244-246°C). In DMSO (deep blue solution), 335 reacts instantaneously with such dienophiles... 

The preparation of selenolopyridazines is accomplished in the usual manner by condensation of diformylselenophenes with hydrazines. Both selenolo[2,3-cf]pyridazine (432) and selenolo[3,"4-tf]pyridazine (433) are obtained in this way (72BSF3453) as crystalline compounds with m.p. 158 and 153 °C, respectively. By strict analogy with the synthesis of boron containing furo- and thieno-pyridines (Sections 3.17.2.3.1, 3.17.3.3.1), boroxazoselenolo-pyridines (e.g. 434) and borazaroselenolopyridines (435,436) could be prepared by condensation of appropriately substituted formylselenophenoboronic acids and hydroxylamine or hydrazine <72IJS(A)(2)257>. 

---