The third member of the cumulenethione series, H2CnS, propadienethione, has been produced by pyrolysis of cyclopenteno-I ,2,3-thiadiazole and detected by microwave spectroscopy which provided rotational parameters for the 32s and 3 4 s isotopomers, the dipole moment [2.064(8) Debye], and an indication that propadienethione is a planar molecule of C2" symmetry.

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Primary alkylamines 1 and hindered arylamines 1 give high yields of isocyanates 5 when reacted with carbon dioxide and the Mitsunobu zwitterions 4 generated from dialkyl azodicarboxylates and Bu 3 P in dichloromethane at -78 °C. Use of Ph 3 P still gave high yields of isocyanates from reactions of primary alkylamines, but only low yields were obtained from reactions of aromatic amines. Reactions which failed to give high yields of isocyanates gave either carbamoylhydrazines 6 and/or dicarbamoylhydrazines 10 and/or triazolinones 7. The triazolinones were shown to arise from reactions of reactive aryl isocyanates with the Mitsunobu zwitterion. The carbamoylhydrazines were shown not to arise from reaction of isocyanate with reduced dialkyl azodicarboxylates, and a mechanism for their formation is proposed. Single-crystal X-ray analyses confirmed the structures of 6, 7, and 10. 3940

The addition of hydrogen cyanide t o alkenes in high yields and with significant amounts (ca. 30%) of asymmetric induction has been achieved when transition metal catalysts with chiral ligands are used. Many asymmetric hydrogenation reactions have been reported,' but in contrast, few examples have been published in which new carbon-carbon bonds have been formed. Two examples where significant asymmetric induction has been achieved are in reactions of norbornene with other akenes2 and in catalytic allylic alkylation~.~ Reaction of hydrogen cyanide with norbornene using a palladium catalyst that we formulate as [( + )-DIOPIPdt gave 2-exocyanonorbornane, [ . I D + 3.4", in which the (lS, 2S, 4R)-(+)enantiomer predominated (SCHEME 1). This was demonstrated by hydrolysis to the corresponding carboxylic acid which had [ . I D + 3.0". The pure (lS, 2s. 4R)enantiomer has [a]D + 10.7"; and thus the optical induction was 28%. SCHEME 1When reactions were carried out with a deficiency of hydrogen cyanide (32 mmol) versus norbornene (64 mmol) in benzene at 130°C in the presence of [( + ) -DIOPIPd (0.09 mmol), the yield of 2-exocyanonorbornane was 40%. This yield increased to 80% when a small amount of free (+ )-DIOP (0.025 mmol) was added. Reaction with this amount of (+ )-DIOP but at a lower temperature, 80T, gave a lower yield (40%) but a slight increase in optical induction (31 %). Reaction Supported by the Australian Research Grants Committee. t DIOP, ~3-O-Isopropylidene-2,3dihydroxy-I.4-bis(diphenylphosphino)butane. 225 WnJ!T23/%0/0333-0225 SO1.75/1@ 1980. NYAS

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