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Dioxaborolanes tartrate-derived

Scheme 10.12 gives some examples of enantioselective cyclopropanations. Entry 1 uses the W.s-/-butyloxazoline (BOX) catalyst. The catalytic cyclopropanation in Entry 2 achieves both stereo- and enantioselectivity. The electronic effect of the catalysts (see p. 926) directs the alkoxy-substituted ring trans to the ester substituent (87 13 ratio), and very high enantioselectivity was observed. Entry 3 also used the /-butyl -BOX catalyst. The product was used in an enantioselective synthesis of the alkaloid quebrachamine. Entry 4 is an example of enantioselective methylene transfer using the tartrate-derived dioxaborolane catalyst (see p. 920). Entry 5 used the Rh2[5(X)-MePY]4... [Pg.933]

The Simmons-Smith cyclopropanation of the same 3-(2-phenylcydopropyl)prop-2-enol (110) in its racemic form afforded an inseparable mixture of and a t/-bicyclopropanes 111 in a 1.3 1 ratio. Therefore, the Charette protocol (p 286) was used first to prepare the required allylic alcohol in its optically pure form and the cyclopropanation was carried out in the presence of the tartrate derived dioxaborolane 93. By using (+)- and (— )-tartrate derived dioxaborolane 93, both the syn- and antf-bicyclopropyls 111 were obtained. The diastereoselectivities observed in their formation were consistently greater than 12 1. ... [Pg.291]

Dioxaborolane derived from dimethyl tartrate has found application in enantioselective epoxidation of unfunctionalized alkenes using TBHP as co-oxidant. [35]... [Pg.49]


See other pages where Dioxaborolanes tartrate-derived is mentioned: [Pg.434]    [Pg.392]    [Pg.85]   
See also in sourсe #XX -- [ Pg.392 ]




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