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4.4.7.2.7.2 Silylative Cyclopropanation

DOI: 10.1055/sos-SD-104-00395

Delvos, L. B.; Oestreich, M.Science of Synthesis Knowledge Updates, (20171148.

In the absence of a copper catalyst, allylic phosphates 223 undergo a silylative cyclopropanation reaction with silylboronic ester 19 promoted by selected stoichiometric bases.[‌24‌] Cyclopropanes 224 are furnished in a highly stereoselective manner and good yields along with only traces of linear allylic silanes 225 (Scheme 91). A base screen showed that potassium hexamethyldisilazanide outperforms other amide or alkoxide bases with regard to product selectivity. Under optimized conditions, representative linear (het)aryl-substituted allylic phosphates are converted cleanly into the trans-diastereomer whereas an alkenyl-substituted precursor reacts with somewhat lower diastereoselectivity. Only a 1-(3,4-methylenedioxyphenyl) substituent at the allylic scaffold leads to a synthetically-less-useful mixture of constitutional isomers. A γ,γ-disubstituted substrate also preferably reacts by cyclization to a cyclopropane bearing a quaternary carbon center. The synthetic work was complemented with mechanistic experiments.

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