3,7-Diiodo- pyridine

A crystalline 5,5 -diene, or bis (vinyl ether), derivative of sucrose has been prepared from 6,6 -dideoxy- 6,6 -diiodo-sucrose hexa-acetate, derived from the 6,6 -ditosylate, by treatment with silver fluoride in pyridine (26). 

Diiodo-l,2-benzenediamine gave 5,8-diiodo-2-(pyridin-2-yl)quinoxaline (131, R = I) [2-(bromoacetyl)pyridine HBr, Me2SO, 60°C, 1 h 20% aerial or solvent oxidation ] 172 perhaps by a comparable mechanism, 1,2-benzenediamine... 

H n.m.r.spectrum of compound 64 showed the well-known allylic coupling 111 between the protons on C-4 and C-6 and C-4 and C-6. On reacting with silver fluoride and pyridine, 2,3,4,l, 3, 4 -hexa-0-acetyl-6,6 -dibromo-6,6 -dideoxysucrose, like the 6,6 -diiodo derivative (63), gave the corresponding 6,6 -dideoxy-5,5 -diene derivative.96... 

Azaborines have received a little attention in recent years, particularly 1,2,3-diazaborines (67) [75ACS(B)1036 76MI2 84MI1] (Scheme 58). Bromine in pyridine converted 5-ethyl-1,2-dimethyl-1,2-dihydro-1,2,3-borazine into a mixture of 4- and 6-monobromo derivatives, and the 4,6-dibromo compound. With iodine monochloride the 4-iodo or 4,6-diiodo products formed, depending on the mole ratio of iodine monochloride to substrate [75ACS(B)461]. 

Iodination of 2-benzyl-2-hydroxypyridine (9.101) occurs at the 6- and subsequently at the 4-position. Under similar conditions, the corresponding N-oxide gave only the 4,6-diiodo product. This does not necessarily prove that the N-oxide function is more effective in activating the 4-position steric hindrance to 6-substitution may be involved (cf. 75CHE478). Whereas both aminomethylation and diazonium coupling were easier for the N-oxide than for 9.101, the 4- 6-isomer ratio for both reactions was similar for both pyridine and its N-oxide (75CHE478). 

A successful procedure involves the treatment of the weakly basic amine in concentrated acid, sulfuric, phosphoric, or glacial acetic, with nittosyl-sulfuric acid. In this manner, the more intractable amines having two or more meta-directing or halogen substituents are subjected to diazotization, e.g., 2,4,6-trinitroaniline (picramide) and 2,6-diiodo-4-nitroaniIine. Pyridine has been used as a solvent in diazotizations with nitrosylsul-furic acid. ... 

Alkynyl derivatives have been prepared by the Stephens-Castro reaction (Scheme 82). 3,5-Diiodo-4( 1H)-pyridinone without 0-protection is monocoupled with phenylethynylcopper. The 5-alkynyl product subsequently suffers Michael attack from the vicinal oxygen function to form a fused product, a furo[3,2-c]pyridine (355) [66JOC4071 87ACSA(B)219 89JCS(P1)1165]. 

The incorporation of two aryl bridgeheads, both linked in turn through the 2,6-substitution of a pyridine nucleus has provided an intermediate which has been converted to a crown ether. Thus, 2,6-bis(2, 6 -dimethoxyphenyl)pyridine after demethylation with boron tribromide or hydrogen bromide in 65% yield was reacted in dimethylsulphoxide containing potassium carbonate with the a,o)-diiodo derivative of triethylene glycol to afford a crown ether system in 22% yield (ref. 199). 

Access to diiodo derivatives of [l,2,3]triazolo[l,5-fl]pyridines is possible using 1 equiv. of the base mixture "TMP-cadmate", which can... 

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