[51694-22-5] · C7H4N2O2Se · o-Nitrophenyl Selenocyanate · (MW 227.09)
(reagent for alkene synthesis2-4)
Physical Data: light brown crystals; mp 139-141 °C.
Solubility: sol common organic solvents such as dichloromethane, THF, DMF, and ethanol.
Form Supplied in: commercially available in 98% purity.
Purification: recrystallization from ethanol.
Handling, Storage, and Precautions: highly toxic and irritant agent. Use in a fume hood.
o-Nitrophenyl selenocyanate is used as an analog of Phenyl Selenocyanate and is a useful reagent for introducing an o-nitrophenylselenenyl group into organic molecules. Advantages of the reagent are: (1) the more facile oxidative elimination ability of the o-nitrophenylselenenyl group than that of a simple phenylselenenyl group (~24 times as fast) (eq 1);2 and (2) the large steric effect of the nitro group at the ortho position which allows enantioselective oxidation of prochiral selenides (eq 2).6 4,4´-Dichlorodiphenyl diselenide is also a useful reagent for alkene synthesis because of its easy access and facile oxidative elimination.2a The yields in elimination reactions of phenyl selenoxides can be improved by a proper choice of reaction conditions.2b
Because of its excellent functional group selectivity and facile elimination ability, the reagent has been widely used for the conversion of primary alcohols into terminal alkenes in the synthesis of numerous natural products. In early applications by Grieco et al., primary alcohols were first transformed to the corresponding bromides or mesylates and then substituted with the o-nitrophenylselenolate anion, which was quantitatively generated by treatment of o-nitrophenyl selenocyanate or di-o-nitrophenyl diselenide with Sodium Borohydride. The substitution products were finally subjected to oxidative rearrangement to afford terminal alkenes (eqs 3 and 4).7,8
More useful methodology for the transformation of primary alcohols to terminal alkenes is the direct reaction with o-nitrophenyl selenocyanate in the presence of Tri-n-butylphosphine to produce the corresponding o-nitrophenyl selenides (eq 5),3 followed by oxidative elimination. This methodology has been extensively employed in the stereoselective synthesis of (±)-antirhine (eq 6),9 in the total synthesis of erythromycin (eq 7),10 and in other syntheses.11
In the presence of tri-n-butylphosphine, o-nitrophenyl selenocyanate reacts with aldehydes to produce cyanoselenenylation adducts. Oxidation of the adducts with Hydrogen Peroxide gives a,b-unsaturated nitriles in high yields (eq 8).4
Oxidation of allylic selenides provides allylic alcohols via 2,3-sigmatropic rearrangement of the allylic selenoxides.12 This rearrangement is useful for the conversion of primary allylic alcohols into the rearranged compounds (eq 9).13
o-Nitrophenylselenolate anions react with epoxides to form ring-opened adducts. These adducts can be easily transformed to ketones by oxidation with hydrogen peroxide (eq 10).14 This methodology is useful for the one-step synthesis of deoxy-keto sugars.14
Like phenyl selenocyanate, o-nitrophenyl selenocyanate reacts with carboxylic acids to give selenol esters in the presence of tri-n-butylphosphine (eq 11),15 but the yield is normally modest.
Michio Iwaoka & Shuji Tomoda
The University of Tokyo, Japan