L-Buten-3-yne

A. E)-(2-Methyl-l,3-butadienyl)dimethylalane. An oven-dried, 1-L, twonecked, round-bottomed flask equipped with a magnetic stirring bar, a rubber septum, and an outlet connected to a mercury bubbler is charged with 7.01 g (24 mmol) of dichlorob1s(n -cyclopentadienyl)z1rconium (Note 2) and flushed with nitrogen. To this are added sequentially at 0 C 100 mL of 1,2-d1chloro-ethane (Note 3), 12.48 g (120 mtiol) of a 5016 solution of l-buten-3-yne in... 

Without the dilution, (Z)-l,4-diphenyl-l-buten-3-yne is detected, apparently formed from the cross-coupling with phenyl acetylide, derived from lithiation of g-bromostyrene, followed by E2cB elimination or Fritsch-Butlenberg-Wiechell type rearrangement. 

Long-range coupling between protons more than two carbon atoms apart is sometimes observed when v bonds intervene. An example is found in l-methoxy-l-buten-3-yne. Not only does the acetylenic proton, Ha, couple with the vinylic proton H, it also couples with the vinylic proton Hc, four carbon atoms away. The data are ... 

Aumann, Rudolf, (l-Alkynyl)carbene Complexes ( = l-Metalla-l-buten-3-ynes) ... 

The hydroboration of enynes yields either of 1,4-addition and 1,2-addition products, the ratio of which dramatically changes with the phosphine ligand as well as the molar ratio of the ligand to the palladium (Scheme 1-8) [46-51]. ( )-l,3-Dienyl-boronate (24) is selectively obtained in the presence of a chelating bisphosphine such as dppf and dppe. On the other hand, a combination of Pdjldba), with Ph2PC6p5 (1-2 equiv. per palladium) yields allenylboronate (23) as the major product. Thus, a double coordination of two C-C unsaturated bonds of enyne to a coordinate unsaturated catalyst affords 1,4-addition product On the other hand, a monocoordination of an acetylenic triple bond to a rhodium(I)/bisphosphine complex leads to 24. Thus, asymmetric hydroboration of l-buten-3-yne giving (R)-allenyl-boronate with 61% ee is carried out by using a chiral monophosphine (S)-(-)-MeO-MOP (MeO-MOP=2-diphenylphosphino-2 -methoxy-l,l -binaphthyl) [52]. 

The complex OsHCl(CO)(P Pr3)2 reacts with 2-methyl-l-buten-3-yne to give the dienyl derivative Os ( )-CH=CHC(Me)=CH2 Cl(CO)(P,Pr3)235 in 86%, which is a result of the selective addition of the Os—H bond of the starting complex to the carbon-carbon triple bond of the enyne (Eq. 4). 

The elongated dihydrogen complex OsCh -fFXCOXP1 Pr3)2 also reacts with 2-methyl-l-buten-3-yne. In toluene at room temperature, the reaction affords the alkenylcarbene derivative OsCl2 CHCH=CMe2 (CO)(P,Pr3)2 in 50% yield, after 1 h (Eq. 7). 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

A completely different approach to butatrienes was reported in 2000 [139]. Treatment of l-aryl-2-bromo-l-buten-3-ynes 195 with a variety of carbon soft nucleophiles 196 in the presence of 5 mol% of a Pd-dpbp catalyst gave the corresponding 1,2,3-butatrienes 197 in moderate yields (Scheme 3.98). The reactions showed essentially no /Z-selectivity all the butatrienes were obtained as mixtures of the two isomers. 

Conversion of l-(AI,N-DiaIkylainino)-3-huten-l-yne into 1 -WJV-TMnlltylniniiMiV -l-buten-3-yne by Reaction with PMnsshnn Amide... 

Z)-l-Methoxy-4-(trimethylsilyl)-l-butene-3-yne (3)1 (b.p. 77-79°/12 mm) is prepared by silylation of 1. Lithiation of 3 at -72° provides the anion a, which reacts with various electrophiles to provide methoxy enynes, (equation I). At higher temperatures a is converted into b, which is useful for preparation of butadiyne derivatives. 

Dichlorobis(triphenylphosphine)-palladium(II), 103 l-Methoxy-l-butene-3-yne, 179 Tetrakis(triphenylphosphine)-palladium(O), 289... 

---