1.3- Dienes. reaction with magnesium

Reactions with Magnesium 175 tetrachloride, yields 5-silaspiro[4,4]-nona-2,7-diene ... 

The starting material can be prepared in known manner from dibenzo[a,d] cyclohepta-1,4-diene-5-one by a Grignard reaction with 3-dimethylaminopropyl magnesium chloride, hydrolysis and dehydration of the resulting carbinol. 

The intermediary formation of the Mg-diene complex is confirmed by a two-step reaction method, namely in the first step a solution of 1,3-diene is electrochemically reduced with magnesium electrode in the absence of the ester. After a sufficient amount of electricity is passed, the current is terminated and the ester is added to the solution. The fact that the coupling product is also formed by this two-step method strongly supports the formation of the intermediate Mg-diene complex. 

S. Akutagawa and S. Otsuka, J. Amer. Chem. Soc., 1976, 98, 7420 the formula for isogeraniol lacks the 6,7-double bond and the diene minor product is named incorrectly. No experimental details are given for the hydrolysis of this myrcene-magnesium complex but the results contradict those reported by Cookson et al. who have extensively investigated its reactions with carbonyl compounds, epoxides, carbon dioxide, and acetonitrile. ... 

The diastereoselective cycloaddition of 2-phenyl-4-dimethylamino-l-thia-3-azabuta-l,3-diene with a choice of dienophiles and in the presence of a Lewis acid provides a convenient route to 5,6-dihydro-4//-l,3-thiazines <2002TL6067, 2004T1827>. The more stable /ra r-adducts are produced exclusively. The approach using (4A)-3-acryloyl-4-benzyloxazolidin-2-one 198 provides access to the chiral 5,6-dihydro-4//-l,3-thiazine 199 <2004T1827>. The exceptional level of selectivity is only achieved when magnesium bromide is used. The chiral auxiliary was removed by reaction with lithium benzoxide to give the benzyl ester 200, and reaction with catalytic amount of samarium triflate and methanol provides the methyl ester 201 (Scheme 21). 2-Substituted-5,6-dihydro-l,3-thiazines are conveniently synthesized from nitriles or thiocyanates and 4-mercapto-2-methylbutan-2-ol to produce... 

Reactions of t-Bu3Si(/-Pr3Si)SiBr2 (20) with activated magnesium or the reagents derived by the reduction of 1,3-dienes with magnesium gave rise to... 

Syn 2-formyl-2-methyl-l,3-dithiane 1-oxide undergoes efficient cycloaddition reaction with Danishefsky s diene with excellent levels of diastereoselectivity in the presence of magnesium bromide at -78 °C (Scheme 9, Table 10). Chelation control models which are similar to those described previously by us, and others,54 were proposed to rationalize the observed stereoselectivity. The proposed model 29 for the syn system is shown below the structure of the major product diastereoi-... 

The compounds obtained by reactions of magnesium with dienes (and anthracene) are classified as special cases of dialkylmagnesium compounds see, for example, p. 40. 

The reaction of magnesium with allyl halides can be a useful method for synthesizing 1,5-dienes by Wurtz-type coupling, e.g. [4],... 

Reactions of the corresponding ketones have been much less studied, but alkylation reactions appear to be highly antiselective relative to the metal. Some alkylations resulting in the isomerization of the diene geometry have been observed. For example, reaction of (85) with methyl magnesium bromide gives (86) but reaction with methyl lithium affords (87) (Scheme 137). Related reductions of dienone iron complexes with sodium borohydride are also highly antiselective. 

Diphenyl-1,3-butadiene has been one of the most reactive conjugated dienes towards metallic magnesium. Reaction of this diene with Rieke magnesium affords (l,4-diphenyl-2-butene-l,4-diyl)magnesium 2, which can be treated with various electrophiles, as shown in Scheme 3. 

A mixture of 153 mg (0.85 mmol) of olivetol, 132 mg (0.87 mmol) of (-i-)-cjs//rans-p-mentha-2,8-dien-l-ol and 200 mg of anhydrous magnesium sulfate in 5 mL of methylene chloride was stirred and cooled to ice bath temperature. Fifty microliters of anhydrous stannic chloride (0.111 g, 0.4 mmol) was added and stirring and cooling was continued. After 10 minutes, the reaction mixture was analyzed by gas-liquid chromatography and shown to contain 30 percent of (-)-6a,10a- rans-l-hydroxy-3-n-pentyl-6,6,9-trimethyl-6a,7,8,10a-tetrahydrodibenzo[b,d]pyran. After quenching the reaction with sodium carbonate, the desired compound can be isolated from the reaction mixture. 

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