The reduction of dimethylaminodichloroborane and dimethylaminodichlorodiborane(4) with NaK2.8 alloy provides the new tetraborane(4) 1 (see scheme). The unusual bonding situation in 1 is explained on the basis of molecular‐orbital calculations.

Bei der Reduktion von Dimethylaminodichlorboran und Dimethylaminodichlordiboran(4) mit NaK2.8‐Legierung wurde das neue Tetraboran(4) 1 erhalten (siehe Schema). Die ungewöhnliche Bindungssituation in 1 wird anhand von Molekülorbitalrechnungen veranschaulicht.

Treatment of 4‐(1,3‐diphenyl‐l‐propynylidene)morpholinium triflate (1a) with the neutral phosphorus nucleophiles Me3Si−PPh2, Me3Si−P(Ph)C5H11, and Me3SiO−PPh2 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 Me3Si−PEt2 and Me3SiO−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 Me3Si−PPh2 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)

For Abstract see ChemInform Abstract in Full Text.

Methyl 2-silabicyclo[2.1.0]pentane-1-carboxylate, obtained by a photochemical intramolecular cyclopropanation reaction of an [small alpha]-allylsilyl-[small alpha]-diazoacetate, undergoes ring opening reactions under different conditions leading to methyl 2-[diisopropyl(methoxy)silylmethyl]cyclopropane-1-carboxylate, a 1-sila-4-cyclopentene-2-carboxylate or an allyl(methoxysilyl)ketene.