Intramolecular nucleophilic assistance at tin: reversal of selectivity in S E2 cleavage of mixed tetraorganotin compounds by iodine

An approach to the C(10)–C(16) fragment of the bryostatins: stereoselective exocyclic double-bond formation by vinyl radical cyclization

“…The major cis-2,6-disubstituted 4-(methoxycarbonylmethylene)tetrahydropyran 50 has functionality and stereochemistry corresponding to the C(10)᎐C (16) fragment of the bryostatins and may be useful for bryostatin synthesis. However, the stereoselectivity of the vinyl radical cyclization was found to depend on the protecting groups used in the synthesis.…”

“…The (E)-isomer of the title compound 37 was a white solid, mp 77-78 ЊC (Found: M ϩ , 506.0898. C 26 H 26 O 3 S requires M, 506.0903); ν max (KBR disc)/ cm Ϫ1 1735, 1621, 1481, 1429, 1253, 1122, 1075, 1060, 1044, 1022δ H 1.68 (3 H, s, 2-CH 3 ), 2.57 (2 H, m, 4-H 2 ), 3.82 (3 H,s,OCH 3 ), 4.06 (2 H, m, 5-H 2 ), 6.40 (1 H,m,m,ArH); m/z (CI) 507 (M ϩ ϩ 1, 8%) and 446 (16).…”

Structural assignment of organotin hydrides containing the oxazoline ligand

“…General procedure for the preparation of tetraorganotin compounds 12,13,15,16 A solution of the o-lithiophenyloxazole prepared by metallation of 2-(4-bromo-phenyl)-4-isopropyl-4,5-dihydro-oxazole (1.39 g, 5.0 mmoles) or 2-(4-bromo-phenyl)-4,5-dihydro-oxazole (1.13 g, 5.0 mmoles) with n-butyl lithium (3.15 ml, 5.0 mmoles, 1.6 M sln in hexane) was slowly added to a solution of R 3 SnX (Ph 2 SnMeI, n-BuMe 2 SnI, Me 3 SnCl, Ph 3 SnCl, 5.0 mmoles) at À70°C and the reaction mixture was stirred for an additional hour and quenched by water. After addition of diethyl ether the organic layer was worked up in the usual manner to give a crude product, which was purified by column chromatography (hexanes/ethyl acetate) to give tetraorganotin compounds 12-16.…”

“…The ease of the bond cleavage could be ascribed to nucleophilic assistance by the imine group, i.e. labilization of the Sn-C bond in a trans position with respect to the coordinating nitrogen atom [12][13][14]. Treatment of tetraorganotin compounds 12 and 14 with excess of bromine in benzene resulted in the formation of the corresponding diorganotin dibromides 21 (65%) and 22 (68%).…”

New chiral tin compounds containing the 2-(4-isopropyl-2-oxazolinyl)-5-phenyl ligand

“…In the case of 7 tin bromide 11 or iodide 12 was formed according to the general rule. Such phenomena could be explained by intramolecular assistance at the tin [10,18]. In view of these results the reported triorganotin bromides and iodides 9-12 were prepared in a much simpler way via addition of stoichiometric amount of bromine or iodine to stannanes 5 and 8 (Scheme 1).…”