Strained olefins hydroboration

Little work has been carried out to probe the reactivity of the double bond of strained olefins by hydroboration. In an early investigation it was found that hydroboration of bicyclo[3.3. l]non-l -ene (69) occurs with low regioselectivity but with reasonable stereospecificity (279 280 281 30 64 6) (252) (Scheme 13). However, it remains to be seen whether 281 is a primary product of the reaction with borane. 

Indeed, 79a, which must exist predominantly in the conformation 79b to avoid A(1 3) strain with the methyl substituent on the olefinic carbon, allows approach of the hydroboration reagent on the face syn to the methyl substituent on the allylic carbon and, thus, the product 80 is formed with a selectivity of 8 1 after oxidative cleavage of the cjc b bond. A similar analysis applies to 81 and guides us to consider 81b as the conformer preferred to 81a. Hydroboration syn-to-methyl on the allylic carbon followed by oxidative cleavage of the crc B bond leads to 82 as the predominant product. Indeed, 82a and 82b are formed in 12 1 diastereoisomeric ratio [37]. 

Hydroboration of trisubstituted olefin is known to give a single product. An alternative to utilize acyclic A-strain effect was demonstrated for high selectivity as shown in Fig. 3, where polar glycol would stay over the sp face so that the... 

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