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1.3.2- Dioxaborolane 2-methyl-, preparation

Racemic l-methyl-2-butenylboronates (E)- and (Z)-3 may be prepared selectively via reactions of the l-methyl-2-butenyl Grignard reagent with the appropriate borate ester. Use of triisopropyl borate provides a 96 4 mixture of (E)-3l(Z)-3 on a 0.36 mol scale15. Use of a bulkier borylating agent, such as 2-isopropyloxy-4,4,5,5-tetramethyl-l,3,2-dioxaborolane, reverses the selectivity, enabling a 91 9 mixture of (Z)-3/( )-3 to be obtained on a 0.5 mol scale. The diastereomeric purity of this mixture may be enhanced to 95 5 by treatment with 0.15 equivalents of benzaldehyde, since ( )-l-mcthyl-2-butenylboronatc ( )-3 is more reactive than (Z)-3. Repetition of this process provides (Z)-3 that is 98% isomerically pure. [Pg.317]

Methyl-l,3,2-dioxaborolan (81) may be prepared by the reaction of BMcs and ethylene glycol at 380 °C ... [Pg.167]


See other pages where 1.3.2- Dioxaborolane 2-methyl-, preparation is mentioned: [Pg.278]    [Pg.318]    [Pg.213]    [Pg.468]    [Pg.1082]    [Pg.27]    [Pg.213]    [Pg.468]    [Pg.353]    [Pg.353]    [Pg.180]    [Pg.63]    [Pg.125]   
See also in sourсe #XX -- [ Pg.39 ]




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