New reactions of allenes, alkynes, ynamides, enynones and isothiocyanates

Abstract

Abstract: This perspective article is related to transformations (both catalytic and non-catalytic) involving allenes, alkynes/enynones/ynamides and isothiocyanates. Part of the work from the author’s group has been reviewed along with some new reactions of (i) allenylphosphonate/allenylphosphine oxide and (ii) a P(III) isothiocyanate. Thus, the allenylphosphine oxide Ph 2P(O)C(Ph)=C=CH 2 undergoes base (DBU) catalyzed addition to the β-ketophosphonate (OCH 2CMe 2CH 2O)P(O)CH 2C(O)CH 3 at 90∘C to afford the addition product Ph 2P(O)C(Ph)=C(Me)CH[C(O)Me][P(O)(OCH 2CMe 2CH 2O)]. In an analogous reaction, with DBU as the base at 140∘C, isomeric vinylphosphine oxides (Z)-Ph 2P(O)C(Ph)=C(Me)CH 2[C(O)Me] and (E)-Ph 2P(O)C(Ph)=C(Me)CH 2[C(O)Me] were isolated. The E-isomer has been characterized by single crystal X-ray structure determination. In another set of studies, the reaction of P(III) isothiocyanate (OCH 2CMe 2CH 2O)P(NCS) with N-(2-bromomethyl)sulfonamide afforded an unusual product with the formula (OCH 2CMe 2CH 2O)P(O)SCH 2CH 2NHS(O) 2-(C 6H 4-4-Me) as shown by X-ray structure determination. This result is different from that obtained in the recently reported analogous reaction using phenyl isothiocyanate. Graphical Abstract: Synopsis. Base-catalyzed the addition of β-ketophosphonate or ethyl acetoacetate to allenylphosphine oxide affords vinylphosphine oxides; in the latter case, elimination of the ester group also takes place. It is also shown that reactivity of a P(III) isothiocyanate is different from that of organic isothiocyanates. [Figure not available: see fulltext.].