2-Butenyl-chloro-di-n-butyltin, in various trans/cis ratios, reacts readily with neat RCHO (R = CH3, C2H5, C2H5(CH3)CH, (CH3)2CH, C6H5) at 25°C to give mixtures of threo/erythro-α-methylallylcarbinols in high yields. The same mixtures are obtained from the equilibrated mixtures obtained by redistribution between Bu3SnC4H7 (C4H7 = trans-, cis-crotyl and α-methylallyl group) and Bu2SnCl2. The reactions are characterized by a high degree of stereoselectivity, especially when bulky R groups are present. The complete allylic rearrangement and the stereoselectivity indicate that an exacyclic transition state is involved. Two stereochemically different transition states lead to two diastereoisomers, threo- and ertythro-α-methylallylcarbinol in the enantioforms RS, SR and RR, SS, respectively
Allylstannation. I. stereochemistry of the addition of trans/cis-2-butenyl-chloro-di-n-butyltin to aldehydes
GAMBARO, ALESSANDRO;MARTON, DANIELE;PERUZZO, VALERIO;TAGLIAVINI, GIUSEPPE
1982
Abstract
2-Butenyl-chloro-di-n-butyltin, in various trans/cis ratios, reacts readily with neat RCHO (R = CH3, C2H5, C2H5(CH3)CH, (CH3)2CH, C6H5) at 25°C to give mixtures of threo/erythro-α-methylallylcarbinols in high yields. The same mixtures are obtained from the equilibrated mixtures obtained by redistribution between Bu3SnC4H7 (C4H7 = trans-, cis-crotyl and α-methylallyl group) and Bu2SnCl2. The reactions are characterized by a high degree of stereoselectivity, especially when bulky R groups are present. The complete allylic rearrangement and the stereoselectivity indicate that an exacyclic transition state is involved. Two stereochemically different transition states lead to two diastereoisomers, threo- and ertythro-α-methylallylcarbinol in the enantioforms RS, SR and RR, SS, respectively
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