Propyne Iminium Salts and Phosphorus( III ) Nucleophiles: Synthesis of (3‐Morpholinoallenyl)phosphanes and ‐phosphane Oxides or 1‐(Morpholinopropargyl)phosphanes and ‐phosphonates

Treatment of 4‐(1,3‐diphenyl‐l‐propynylidene)morpholinium triflate ( 1a ) with the neutral phosphorus nucleophiles Me 3 Si−PPh 2 , Me 3 Si−P(Ph)C 5 H 11 , and Me 3 SiO−PPh 2 affords (3‐morpholinoallenyl)phosphanes 4 and 5 and (3‐morpholinoallenyl)phosphane oxide 11 , respectively. In contrast to these conjugate addition reactions at the ambident propyne iminium moiety of 1a , nucleophilic attack by Me 3 Si−PEt 2 and Me 3 SiO−P(OEt) 2 takes place at the iminium function and gives (1‐morpholinopropargyl)phosphane 6 and (1‐morpholinopropargyl)phosphonate 12 , respectively. Propyne iminium salt 1b reacts with Me 3 Si−PPh 2 to form (3‐morpholino‐1,3‐butadienyl)phosphane oxide 8 . The bis(donor)‐substituted allene 4 is transformed by oxidation of the phosphorus substituent into the push‐pull substituted allenylphosphane oxide 11 . Treatment of allene 4 with elemental sulfur results in the formation of betaine 16 , which undergoes [3+2] cycloaddition reactions with acetylenic esters to afford 5‐benzylidene‐4,5‐dihydrothiophenes 17 and 18 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)