Alkenyl reagents, reactions

In addition to alkenylboron compounds, alkenylalane, alkenylzirconium, alkenyltin, alkenyl copper, and alkenylmagneslura reagents are reported to undergo a related alkenyl-alkenyl coupling reaction to give l,3-a1kad1enes. 

Stereoselective syntheses of trisubstituted alkenes are based on E- and Z-alkenyl-dioxaborinanes. Reaction with an alkyllithium reagent forms an ate adduct which rearranges on treatment with iodine in methanol.30... 

The (R) allene 121 was obtained with high anti stereoselectivity in the reaction of (i )-(—)-l-trifluoroacetoxy-l-phenyl-2-propyne (120) with PhZnCl. 2-Alkynyloxiranes react smoothly with alkynyl, alkenyl and arylzinc reagents. Reaction of 2-methyl-2-(l-propynyl)oxirane (122) with vinylzinc chloride (123) yields 2,4-dimethyl-2,3,5-hexatrien-l-ol (124) [31],... 

Aluminum Reagents. Alkenylalnminnm compounds can also be used as reagents for alkenylation in reactions promoted by palladium. Formation of a 2-alkenylpyridine 216 is shown (Scheme 82). 

These early reports [18, 20] provide support for the proposed role of Pd in stoichiometric synthesis of benzofurans involving reaction of pallada(ll)cyclic Pd(L-C,C)(bpy) (L = [2-(Et02CCH0)C6H4] )with l(C=CR)Ph(BF4) [69, 70], Palladium(IV) intermediates were not detected in this study, but NMR monitoring of reactions of closely related alkenyl reagents I(CH=CHR)Ph(BF4) led to detection of a Pd - intermediate [69, 70],... 

Allylic alcohols of use in the synthesis of deoxy sugars have been synthesized by reaction of 4-deoxy-L-erythrose derivative (47) (available from the products of cinnamaldehyde in fermenting bakers yeast) with various metal-alkenyl reagents the major isomer (48), formed with vinylmagnesium bromide, was thus converted into the 6-deo3Qr-L-altrofuranosides (49) (Scheme 9). Full details on the synthesis of 2-deojy-L-sugars from l-... 

The 3-pyridyl Grignard reagent has been alkenylated by reaction with allyl halides and the 2-picolyl Grignard reagent homologated with alkyl halides and to-diethoxyalkyl halidesi . Of much greater importance has been the use of picolyl lithium, potassium and sodium compounds in reactions with alkyl and aralkyl halides. 

Scheme 5-95. Propargyl-alkenyl coupling reactions of zinc reagents.

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

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