Control of regioselectivity in reactions of dialkylstannylene acetals. Part I. A dramatic reversal of regioselectivity in mono-p-toluenesulfonation reactions

Abstract

The regioselectivities of p-toluenesulfonation reactions of dialkylstannylene acetals obtained from a number of carbohydrate-derived terminal 1,2-diols in the absence of added nucleophiles have been explored as functions of the carbohydrate structure, the nature of the alkyl group on tin, the solvent, and the reaction temperature. Virtually all dibutylstannylene acetals react preferentially on the primary oxygen atom, sometimes with excellent regioselectivity. Increasing the steric bulk of the alkyl substituents on tin increases the preference for reaction at the secondary oxygen atom, but at the expense of increased reaction times. Hexamethylenestannylene acetals react at about the same rate as dibutylstannylene acetals; in almost all cases, they react preferentially on the secondary oxygen atom, sometimes with excellent regioselectivity.

Stereoselective Total Synthesis of (‐)‐Ebelactone A

“…After obtaining alcohol 12 , our next aim was to introduce a methyl group at C‐13 carbon. To this end, the primary hydroxyl group of compound 12 was tosylated using p ‐toluenesulfonyl chloride (Ts−Cl), triethylamine and 4‐dimethylaminopyridine (DMAP) in dry CH 2 Cl 2 at 25 °C to afford 13 in 81 % yield . The tosyl compound 13 was subjected to Gilman's alkylation with 6.0 eq.…”

“…To this end, the primary hydroxyl group of compound 12 was tosylated using p-toluenesulfonyl chloride (TsÀ Cl), triethylamine and 4-dimethylaminopyridine (DMAP) in dry CH 2 Cl 2 at 25°C to afford 13 in 81 % yield. [11] The tosyl compound 13 was subjected to Gilman's alkylation [12] with 6.0 eq. of dimethyllithiumcuprate (Me 2 CuLi) in Et 2 O at À 20°C to give methylated product 14 in 90 % yield.…”

Carbohydrate-derived conformationally restricted bicyclic dipeptides as potential hetero foldamer building blocks

“…The cis-stereochemistry of the b-lactam was readily indicated by the coupling constants (J = 5-6 Hz), which is characteristic of cis-b-lactams. 14 Deprotection of acetonides 5a-d cleanly furnished diols 6a-d, which were then subjected to selective dibutyltin oxide-mediated tosylation 15 to afford the O-tosyl derivatives 7a-d in excellent yields. Azide reduction within 7a-d with concomitant Boc protection cleanly afforded the cyclized target building blocks 1a-d in excellent yield (93-96%), without the requirement for special conditions for effecting cyclization.…”

Total Synthesis of (+)‐Bourgeanic Acid Utilizing Desymmetrization Strategy

“…[6] The chemoselective protection of 1,3-diol 4 using 2,2-DMP, pTsA (catalytic) in acetone:ether (9:1) afforded the corresponding acetonide 8 in 83 % yield, [8] which was confirmed by the 13 C NMR spectrum analysis (δ = 98.0 ppm for the acetonide carbon flanked by two oxygen atoms). Tosylation of primary alcohol 8 using TsCl, Et 3 N, DMAP in CH 2 Cl 2 afforded the tosylate 9 in 86 % yield, [9] 1 H NMR spectrum of the compound 9 revealed the presence of two ortho aromatic protons resonating as doublet at δ = 7.76 ppm, and the methyl protons of the tosyl group at δ = 2.45 ppm as a singlet. Then compound 9 was subjected to Gillman's reaction with 6.0 equiv.…”