Aryl selenocyanates

The carbon-nitrogen triple bond of aryl thiocyanates acts as a dipolarophile in 1,3-dipolar cycloadditions. Reactions with nitrile oxides yield 5-arylthio-1,2,4-oxadiazoles 227 (X = O Y = S). Aryl selenocyanates behave similarly forming 5-arylseleno-l,2,4-oxadiazoles 227 (X = 0 Y = Se). Reactions of 5-aryl-... 

Alkyl phenyl setenides selenol esters. N-PhcnylscIcnophthalimidc is superior to aryl selenocyanates for conversion of alcohols to alkyl phenyl selenides (6, 252-253) and of carboxylic acids to selenol esters (7, 396-397). When conducted in the presence of an amine the latter reaction provides amides in high yield (equation l). ... 

Alkyl selenides are most conveniently prepared by the dialkylation of Na2Se or by the monoalkylation of selenolates. Common routes to aryl derivatives include the reaction of a selenolate with a diazonium salt, the SrnI reactions described earlier, and the reaction of aryUithiums with aryl selenocyanates (ArSeCN). A different approach employs the reaction of alcohols with aryl selenocyanates or N-(phenylseleno)phthalimide (see Section 6) in the presence of tri-n-butylphosphine. Similar conditions can also be used to convert carboxylic acids to selenoesters (8). These reactions are illustrated in Scheme 3. 

It has been reported that aryl selenocyanate (25 Scheme 7) reacts with carboxylic acids in the presence of tributylphosphine under mild conditions, giving rise to selenol esters in good yields. The process may involve the reaction of carboxylic acids with selenophosphonium salt (26), which is the key intermediate. 

Displacement of OH by an ArSe group. Reaction of aryl selenocyanates with alcohols, aldehydes or carboxylic acids to give alkyl aryl selenides, homologation of aldehydes or esters of arylselenols. 

Cyanosehnenylation of aldehydes. Aldehydes react with aryl selenocyanates in the presence of tri-n-butylphosphine in THF at 20° to form cyano selenides in 75-99% yield (equation I). Ketones do not undergo this reaction. The products can be used for a variety of transformations, as formulated in equations (II) and (HI). 

Aryl selenocyanates. - These substances have usually been prepared by diazotization of an arylamine followed by reaction of the diazonium salt with KSeCN cf. 6, 420-421). Japanese chemists have reported an alternate method reaction of an aryl iodide with KSeCN in HMPT at 100-120° with catalysis by Cul. Yields are only modest to good. 

Preparation of Thiocyanates.—Variations of standard methods for the synthesis of thiocyanates are illustrated in the addition of alkoxy- and thiocyanato-groups to alkenes using KSCN, CuClj (or other Cu salt), and an alcohol as solvent, to give a-alkoxy-alkyl thiocyanates and in the addition of pseudohalogens CISCN or (SCN)a to chalcones. A sulphonylthiocyanate RSOaSCN, prepared from (SCN)a and a sodium sulphinate, adds similarly to alkenes to give a-thio-cyanato-alkyl sulphones. > Aryl selenocyanates may be prepared from the... 

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