Epoxide regioselective ring-opening

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

The regioselective ring opening of the silyl epoxides is facilitated by the stabilizing effect that silicon has on a positive charge in the -position. This facile transformation permits vinylsilanes to serve as the equivalent of carbonyl groups in multistep synthesis.149... 

The regioselective ring-opening of epoxides 34 (R1 = Me, vinyl, Ph etc.) with aminolead compounds R23 PbNEt2, prepared from lithium diethylamide and R23 PbBr, gives good yields of the amino alcohols 3567. 

The regioselective ring-opening of the chiral epoxides 36 (R1 = Me, Pr or Ph) with aliphatic amines 37 (R2 = t-Bu, PI1CH2 or C6H13) in the presence of titanium tetraiso-propoxide leads to mixtures of the amino alcohols 38 and 39, in which the former predominate70. 

Epoxidation of amino chalcone 17, followed by regioselective ring opening of the epoxide unit, demonstrates the formation of optically active lactam derivatives of type 18, which are highly important structures for use within the pharmaceutical industry. The reaction proceeds in good yield and without loss of stereochemical integrity (Scheme 15). 

Reddy, M. A. Surendra, K. Bhanumathi, N. Rao, K. R. Highly facile biomimetic regioselective ring opening of epoxides to halohy-drins in the presence of /J-cyclodextrin. Tetrahedron 2002, 58, 6003-6008. 

The epoxidation of the carbon-carbon double bond in ethyl 3-methyleneazetidine-l-carboxylate 46 using w-chloroperbenzoic acid and the regioselective ring opening of the resulting epoxide 47 with HBr and HC1 led to the synthesis of ethyl 3-bromomethyl-3-hydroxyazetidine-l-carboxylate 48 and ethyl 3-chloromethyl-3-hydroxyaze-tidine-l-carboxylate 49, respectively (Scheme 8) <1997JOC4434>. 

Regioselective ring opening of the epoxide in 200 occurs in the presence of bromine and triphenylphosphine to give the bromohydrin 201 (R = Br), which on treatment with azobisisobutyronitrile (AIBN) and tributyltin hydride gives the c o-6-hydroxy-2-azabicyclohexane 201 (R = H) <2001JOC1811>. The 5-substituted derivatives of alcohol 201 (R = Me or Ph) are obtained by treatment of 200 with lithium dimethylcopper or lithium diphenylcopper <20040L1669>. 

Preparation of enantiometrically pure aldehyde substrates for DHAP-dependent aldolase reactions has been accomplished by a combination of enzymatic and chemical methods. The lipase-catalyzed resolution of racemic aldehyde precursors has been accomplished by enantioselective acetate hydrolysis, as exhibited in the preparation of enantiomerically pure R- and S -glycidaldehyde acetals (Scheme 5.10).31 Regioselective ring opening of the epoxides, followed by acetal hydrolysis, generated the aldehydes in enantiomerically pure form. 

Tabatabaeian, K., Mamaghani, M., Mahmoodi, N.O., and Khorshidi, A. 2008. Solvent-free, ruthenium-catalyzed, regioselective ring-opening of epoxides, an efficient route to various 3-alkylated indoles. Tetrahedron Letters, 49 1450-54. 

Alkyl stannyl selenides are also useful nucleophilic selenium reagents. Tri-methylstannyl or tributylstannyl methyl selenides 58 react with halides 59 to produce unsymmetrical selenides 60 in good yields in the presence of a fluoride ion or by treatment with n-butyllithium (Scheme 44) [84]. Tributylstannyl phenyl selenide (61) reacts smoothly with acetals to give monoselenoacetals 62 in the presence of boron trifluoride etherate (Scheme 45 a) [85]. Similar reaction conditions were applied to the regioselective ring opening of epoxides (Scheme 45b) [86]. 

The regioselective ring opening of 2,3-epoxy acids can also be achieved (Eqs 269 and 270) [616]. The titanium-promoted reaction always favors C3 opening of the epoxides whereas in the absence of Ti(0-i-Pr)4 the same reaction proceeds with much lower or even reversed regioselectivity. The same tendency was observed for the reaction of 2,3-epoxy amides [616]. 

CH2CI2 to THF allowed protected diethyl l-(phenylsulfonyl)-3-hydroxy-4-iodobutylphosphonate to be prepared directly from the epoxide (Scheme 4.51). This reaction presumably proceeds via the generation in situ of iert-butyldimethylsilyl iodide. Similarly, diethyl 1-(ethoxycarbonyl)-3,4-epoxybutylphosphonate undergoes regioselective ring opening at C-4 by amines in DMF at 50°C. ... 

---