1- Propynylmagnesium bromide

Compared to the reaction in exp. 30, the conversion of 2,3-dibromotetrahydrofuran with propynylmagnesium bromide can be carried out at higher temperatures, so that the reaction time can be shortened to 2 h at 50 C. When propynyUithium is used instead of the Griguard reagent, a very impure product is obtained in low yield. Elimination possibly predominates with the more strongly basic lithium alkynylides (compare exp. 28). 

Butyn-l-ol has been prepared as above for the first stage3>4 6 but using aqueous sodium hydroxide 3 and alcoholic potassium hydroxide 6 for the second stage. Earlier workers 6 7 employed the reaction between propynylmagnesium bromide and formaldehyde. 

Some unreacted magnesium turnings remain in the flask at this time. However, the submitters recommend against heating the mixture to achieve further conversion, since the initially formed allenylmagnesium bromide will isomerize to 1 -propynylmagnesium bromide. 

These two / f( -reactions have been used for a stercospecific synthesis of dihydrone-petalactone (7) from norbomenone (3).- Addition of propynylmagnesium bromide, followed by Lindlar reduction of the triple bond, acetylation, and reaction with 2. provides the allylsilane 4. Epoxidation of 4 and dcsilylation results in 5. Oxy-Cope rearrangement of 5 results in a single ketone (6) with the desired four chiral centers. The remaining steps to 7 involve conventibnal reactions. 

The second iteration is accomplished by the addition of propynylmagnesium bromide to aldehyde (168) the 1 1 mixture of diastereomers is separated and treated as in Scheme 14. ... 

The synthesis of 3,4-substituted anisoles [for example, R = R = (CH2)4] has been effected in the manner shown by the reaction of propynylmagnesium bromide with a sulphur-containing a,p-unsaturated ketone derivative to afford an intermediate carbinol. Cyclisation of this with boron trifluoride-etherate in the presence of methanol occurred with loss of methylthiol and desulphurisation by means of Raney nickel gave the final product (ref.86). The same sulphur-containing intermediates have been used with aryl esters to derive 4-methoxy acetophenone (ref. 87,88). Carbonyl derivatives of phenols are considered in detail in Chapter 7. 

Epoxy-l,3,5-cyclooctatriene added dropwise with ice-cooling to a soln. of propynylmagnesium bromide prepared from propyne and ethylmagnesium bromide in abs. ether, stirred 2 hrs. at room temp, and 1 hr. under reflux -> l-(2,4,6-cycloheptatrien-l-yl)-2-butyn-l-ol (Y 75%) dissolved in dimethylformamide, ice-cooled, treated dropwise with a soln. of SOClg in dimethylformamide, and stirred 1 hr. at room temp. l-phenyl-l-penten-3-yne (Y 87%). F. e. s. J. Hambredit, H. Straub, and E. Muller, B. 107, 2985 (1974). 

---