Synthesis of 1-hydroxybicyclo[n.1.0]alkanes (n = 3 and 4) and their silyl ethers from olefinic esters via tandem intramolecular nucleophilic acyl substitution and intramolecular carbonyl addition reactions mediated by reagent

Additive Tuned Selective Synthesis of Bicyclo[3.3.0]octan-1-ols and Bicyclo[3.1.0]hexan-1-ols Mediated by AllylSmBr

The selective construction of bicyclo[3.3.0]octan-1-ols and bicyclo[3.1.0]hexan-1-ols was achieved by using an allylSmBr/additive(s) system. By employing HMPA as the only additive, the momoallylation/ketone-alkene coupling occurred preferably and afforded bicyclo[3.3.0]octan-1-ols in good yields with high diastereoselectivities. While the ester-alkene coupling predominated to generate bicyclo[3.1.0]hexan-1-ols in moderate yields with excellent diastereoselectivities in the presence of a proton source, such as pyrrole as the coadditive with HMPA. The tunable reactivity of allylSmBr by additive(s) would make it a versatile reagent in organic synthesis.

Highly Regioselective Coupling Reactions of Allylic and Propargylic Alcohol Derivatives with γ,γ-Dialkoxyallylic Zirconium Species via Zr-to-Cu Transmetalation

In the presence of CuCN, reaction of gamma,gamma-dialkoxyallylic zirconium species 4, generated in situ by treating triethyl orthoacrylate with zirconocene-butene complex, with allylic and propargylic phosphates proceeded at the alpha-position of 4 in a highly SN2'-selective manner to give the corresponding 5-alkenoates and 4,5-alkadienoates, respectively. In the present Cu(I)-mediated coupling reaction, the gamma,gamma-dialkoxyallylic zirconium species 4 serves as a synthetically useful homoenolate anion equivalent of propionate.

Radical fragmentation of omega-bromoalkyl cyclobutanones. A modular approach to eight-membered carbocycles

[reaction: see text] An eight-membered ring was conveniently appended onto a cycloalkene carboxylate by employing a facile radical cyclization-fragmentation reaction of an omega-bromoalkyl spirocyclobutanone, which was readily accessible by the Kulinkovich cyclopropanation and subsequent electrophilic addition to a 3-bromoalkyl acetal.

A theoretical study on the mechanism and diastereoselectivity of the Kulinkovich hydroxycyclopropanation reaction

A detailed mechanism for the Kulinkovich hydroxycyclopropanation reaction has been explored with density functional theory calculations on the reactions between R(1)COOMe and Ti(OMe)(2)(CH(2)CHR(2)) (R(1) and R(2) are hydrogen and alkyl groups). Addition of ester to titanacyclopropane is found to be fast, exothermic, and irreversible. It has a preference for the alpha-addition manifold over the beta-addition manifold in which its cycloinsertion transition states suffer from the steric repulsion between the R(2) and ester. The following intramolecular methoxy migration step is also exothermic with reasonable activation energy. The cyclopropane-forming step is the rate-determining step, which affords the experimentally observed cis-R(1)/R(2) diastereoselectivity in the alpha-addition manifold by generating cis-R(1)/R(2) 1,2-disubstituted cyclopropanol when R(1) is primary alkyl groups. On the contrary, the unfavored beta-addition manifold offers the diastereoselectivity contradicting the experimental observations. The effects of R(1) and R(2) on the regio- and stereoselectivity are also discussed.

Intramolecular Nucleophilic Acyl Substitution Reaction of 3,4-Alkadienyl Carbonates Mediated by Ti(O-i-Pr)(4)/2 i-PrMgCl Reagent. Efficient Synthesis of Optically Active beta,gamma-Unsaturated Esters with an alpha-Substituent

Treatment of 3,4-alkadienyl carbonates 2a-i with a low-valent titanium reagent diisopropoxy(eta(2)-propene)titanium (1), readily generated by the reaction of Ti(O-i-Pr)(4) with 2 i-PrMgCl, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford vinyltitanium compounds 3 which, in turn, reacted with H(3)O(+), D(2)O, or iodine to give alpha-substituted beta,gamma-unsaturated esters 4 in good to excellent yields. The olefin moiety of the hydrolysis product 4 has (Z)-geometry mainly except for 4h. Starting from chiral 2f or 2g, the reaction proceeded stereospecifically to give optically active alpha-substituted beta,gamma-unsaturated ester 4f or 4g having (Z)-olefin geometry exclusively.