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R e a r r a n g e m e n t R e a c t i o n s ; 1 2 : 1 S y n t h e s i s a n d R e a c t i o n s o f I s o t h i o c y a n a t e S u b s t i t u t e d Abstract: The first method for the preparation of isothiocyanate substituted allenes by [3,3] sigmatropic rearrangement of propargyl thiocyanates is described. These allenes undergo a variety of successive reactions such as ionic or sigmatropic isomerization, electrocyclic ring closure, cycloaddition, and electrophilic addition. Furthermore, intramolecular nucleophilic attack as well as treatment with external nucleophiles lead to heterocyclic products.

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Treatment of allenyl isothiocyanates with sulfur-, oxygen-, nitrogen-or hydride-containing nucleophiles such as propane-2-thiol, thiophenol, hydrogen sulfide, alcohols, phenol or aqueous NaOH, NH 3 , primary or secondary aliphatic or aromatic amines, N,N,N¢,N¢-tetramethylguanidine or sodium cyanoborohydride resulted in ring closure to generate thiazoles bearing a functionality at position C-2 in most cases. Moreover, we report the first examples of aromatic thiazole-2-phosphonates prepared by the same strategy using dialkyl or diphenyl phosphites as nucleophiles.Recently, we reported 2 that the well known 3 isomerization of allyl thiocyanate to allyl isothiocyanate can be transferred to propargyl thiocyanates 1 as an alternative starting material yielding allenyl isothiocyanates 2 (Scheme 1). However, in general this [3,3]-sigmatropic rearrangement 1 → 2 can be performed only by the technique of flash vacuum pyrolysis (FVP) successfully because neat (undiluted) cumulenes, such as 2, tend to exothermic spontaneous polymerization even at room temperature. Whereas allenyl isothiocyanates like 2a and 2b can be obtained nearly quantitatively in hundred-gram batches per day, there are some limitations in other cases such as 2c and 2d. Flash vacuum pyrolysis of 1c leads to equilibrium with 2c (ratio 1c/2c = 17:83) while rearrangement 1d → 2d is nearly irreversible. However, the yield of 2d is limited to 73% since the precursor 1d cannot be vaporized without decomposition.We present now the reactions of the isothiocyanates 2 with sulfur-, phosphorus-, oxygen-, nitrogen-and hydride-containing nucleophiles leading to thiazole 4 derivatives. Thus, the chemistry of 2 illustrates that allenyl isothiocyanates act predominantly as synthetic equivalents of synthons 3.

Ungewöhnlich reaktiv gegenüber Nucleophilen sind die Allenylisothiocyanate 1 (R1,R2 = H oder Me), die über [3,3]‐sigmatrope Umlagerungen aus leicht zugänglichen Propargylthiocyanaten hergestellt werden können. Über ähnliche Isomerisierungsreaktionen gelingt auch die Herstellung von 2 und 3 (R = H, Me), Diese Verbindungen eignen sich für die Synthese von Heterocyclen und für Cycloadditionsreaktionen.