Stereoselective 4-Benzyloxybut-2-enylation of Aldehydes via an Allyl-Transfer Reaction Using a Chiral Allyl Donor

Abstract

[reaction: see text] A direct and highly stereoselective (E)-4-benzyloxybut-2-enylation of aldehydes was successfully carried out to give 5-benzyloxyhomoallylic alcohol (11) via an allyl-transfer reaction using a chiral allyl donor (10). The chiral allyl donor (10) was prepared by catalytic Sharpless asymmetric epoxidation of 3-methylbut-2-en-1-ol, followed by a stereospecific vinyl Grignard reaction of the epoxide in the presence of CuBr and selective benzylation of the primary alcohol of diol.

Diastereoselective Allylation of Carbonyl Compounds and Imines: Application to the Synthesis of Natural Products

“…The allyl transfer from this donor to different aldehydes allowed the stereoselective preparation of 5-benzyloxyhomoallylic alcohols. 131 As shown in Scheme 50, the transfer of chirality was excellent when different aliphatic aldehydes were used in the presence of triflic acid as catalyst, including the sterically hindered pivalaldehyde. Importantly, when the (R)-allyl donor was used, the major product has (S,E)-configurations, the (R,Z)-product being detected as the minor isomer.…”

Catalytic Nucleophilic Allylation Driven by the Water–Gas Shift Reaction

“…The spectroscopic data matched those from the literature. 70 Data for 10c : 1 H NMR (500 MHz, CDCl 3 ) 7.31–7.26 (m, 2H, C(aryl)H), 7.22–7.17 (m, 3H, C(aryl)H), 5.82–5.65 (m, 2H, C(3)H, C(4)H), 4.15–4.09 (m, 2H, C(5)H 2 ), 3.71–3.64 (m, 1H, C(1)H), 2.80 (dt, J = 13.6, 8.0 Hz, 1H, C(1′)H a ), 2.68 (dt, J = 13.7, 8.1 Hz, 1H, C(1′)H b ), 2.37–2.24 (m, 1H, C(2′)H a ), 2.25–2.13 (m, 1H C(2′)H a ), 2.08–1.90 (m, 2H, br C(1)OH, br C(5)OH), 1.84–1.73 (m, 2H, C(2)H 2 ); 13 C{1H} NMR (125 MHz, CDCl 3 ) 142.1, 132.7, 128.6, 128.6, 128.5, 126.0, 70.4, 63.5, 40.5, 38.7, 32.1; MS (ESI) 229.0 (MNa + , 100); TLC R f 0.253 (Et 2 O/CH 2 Cl 2 , 4:1) [UV, KMnO 4 ].…”

Air‐Stable Bifunctional Allylation Reagents for the Asymmetric Synthesis of Differentiated syn‐ and anti‐1,3‐Diols

“…In recent years, acid‐catalyzed asymmetric allyl‐transfer reactions,4 which follow a [3,3]‐sigmatropic rearrangement mechanism, have emerged as an alternative to more traditional aldehyde allylation reactions often employing sensitive chiral allyl–metal reagents or intermediates 5. Particularly appealing in the context of our on‐going research was Nokami et al.’s recent report that described Brønsted acid catalyzed asymmetric allylation of aldehydes by an “organic” chiral allyl‐transfer reagent to give homoallylic alcohols with near‐perfect chirality transfer and high E / Z selectivity (Scheme ) 6…”

“…Enantiomerically pure ( ee >99 %) 2 was obtained by washing the crude 2 with diethyl ether. Reaction of 2 with vinylMgCl in the presence of CuBr ⋅ SMe 2 at −20 °C furnished diol 3 ,6 which upon treatment with PMP chloroformate and pyridine transformed into I . Compound I (and ent ‐ I ) is stable at ambient temperature and can be stored without any special precautions.…”

“…[5] Particularly appealing in the context of our on-going research was Nokami et als recent report that described Brønsted acid catalyzed asymmetric allylation of aldehydes by an "organic" chiral allyl-transfer reagent to give homoallylic alcohols with near-perfect chirality transfer and high E/Z selectivity (Scheme 1 a). [6] We recently disclosed Ir I -catalyzed enantioselective decarboxylative allylic etherification of para-methoxyphenyl (PMP) allyl carbonates as a general method for the asymmetric synthesis of PMP-protected allyl alcohols (Scheme 1 b). [7][8][9] We envisioned that merging Nokami et als allyl-transfer reaction with our decarboxylative allylic etherification reaction could create a new "organic" chiral bifunctional reagent I, which could undergo the reactions in Scheme 1 a,b without recourse to functional-group adjustments to give differentiated 1,3-diols with complete stereochemical control (Scheme 1 c).…”