[2955-74-0] · C9H10N2O7S · p-Nitrobenzenesulfonyloxyurethane · (MW 290.28)
Physical Data: mp 116.4-116.8 °C.
Solubility: sol ether, acetone, CHCl3, CH2Cl2, DMSO, DMF, ethyl acetate, alcohols; moderately sol benzene; insol hydrocarbon solvents, CCl4, H2O.
Preparative Method: by the reaction of N-hydroxyurethane with p-nitrobenzenesulfonyl chloride.2
Treatment of the title compound with a base such as Triethylamine leads to deprotonation followed by a-elimination to generate singlet ethoxycarbonylnitrene.2,3 The mild conditions required offer an advantage over Ethyl Azidoformate as a source of the ethoxycarbonylnitrene. The synthetic utility of this nitrene is limited to two types of reactions: (1) aziridination of alkenes and (2) addition to heteroatoms, which is often followed by rearrangement. A common side-reaction is the insertion of the nitrene into C-H bonds. The synthetic utility of the insertion reaction itself is severely limited since ethoxycarbonylnitrene shows poor selectivity toward different types of C-H bonds. The development of procedures to generate this nitrene under phase-transfer conditions has enhanced its utility.4,5
Ethoxycarbonylnitrene generated by a-elimination adds to alkenes to give the corresponding aziridines in moderate yields. Thus reaction of ethoxycarbonylnitrene with the strained alkene 2-azabicyclo[2.2.0]hex-5-ene under phase-transfer conditions produces the aziridine in 42% yield (eq 1).6 Thermolysis of the adduct gives rise to a 1,4-diazepine. This method has been used to access a variety of substituted 1,4-diazepines, 1H-1,4-diazepines,7 and other heterocyclic ring systems.8
Addition of ethoxycarbonylnitrene across the double bond of a symmetric propelladiene has been reported to give a mixture of stereoisomeric aziridines in 46% yield.9 Additions to vinylsilanes under phase-transfer conditions10 and to vinyl chlorides11 produce the corresponding aziridines in moderate yields. Addition to azo compounds yields azimines which, on subsequent photolysis, give the triaziridines.12 Aziridination of isolated double bonds occurs preferentially over the double bond of allylic ethers.13 Attempted addition to enamines14 and allenes15 gives very low yields of the desired products. Addition to a chiral, optically active enol ether has been reported to proceed in low yield, but with high diastereoselectivity.16 Additions to allylic and homoallylic acetals have also been reported.17
There are few examples of synthetically useful reactions involving addition of ethoxycarbonylnitrene to heteroatoms. Addition to phospholes gives the corresponding iminophospholes in good yield.18 Addition of ethoxycarbonylnitrene to trialkylboranes gives the corresponding N-alkyl carbamates after rearrangement and hydrolysis (eq 2).19 This procedure allows access to a variety of ethyl N-alkylcarbamates in high yields.
William H. Pearson & P. Sivaramakrishnan Ramamoorthy
University of Michigan, Ann Arbor, MI, USA