Concerning the 1,5-stereocontrol in tin(iv) chloride promoted reactions of 4- and 5-alkoxyalk-2-enylstannanes: trapping intermediate allyltin trichlorides using phenyllithium

Abstract

Transmetallation of the 5-benzyloxy-4-methylpent-2-en-1-yl(tributyl)- and -(triphenyl)stannanes 1 and 8 using tin(iv) chloride generates an allyltin trichloride that reacts with aldehydes to give (Z)-1,5-anti-6-benzyloxy-5-methylhex-3-en-1-ols 2. The allyltin trichloride believed to be the key intermediate in these reactions has been trapped by phenyllithium to give anti-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 9. Transmetallation of this anti-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 9 generated an allyltin trichloride that reacted with aldehydes to give the (Z)-1,5-syn-6-benzyloxy-5-methylhex-3-en-1-ols 23 and was trapped by phenyllithium to give syn-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 24. Similar stereoselectivity was observed for tin(iv) chloride promoted reactions of this syn-5-benzyloxy-4-methylpent-1-en-3-yl(triphenyl)stannane 24 with aldehydes and with phenyllithium. The allyltin trichlorides generated by transmetallation of 4-hydroxy- and 4-benzyloxy-pent-2-enyl(triphenyl)stannanes 34 and 35 were similarly trapped by phenyllithium to give 4-hydroxy- and 4-benzyloxy-pent-1-en-3-ylstannanes 36 and 37 whose configurations were established by correlation with known compounds. This work confirmed the configurations of the intermediate allyltin trichlorides involved in tin(iv) chloride promoted reactions of 4- and 5-alkoxypent-2-enylstannanes with aldehydes and showed that the high levels of remote stereocontrol were due mainly to kinetically controlled transmetallation. A fuller mechanistic scheme is proposed for the reactions in the 5-benzyloxy-4-methylpent-2-enylstannane series together with relevant (119)Sn NMR data.

An approach to aliphatic 1,8-stereocontrol: diastereoselective syntheses of (±)-patulolide C and (±)-epipatulolide C

“…C 17 H 34 NSiO 3 requires M, 328.2308); ν max /cm −1 3308, 2953, 2893, 2116, 1642, 1423, 1374, 1249, 1080, 1025, 931, 860, 836, 758 and 693; δ H (300 MHz, CDCl 3 ) 0.00 (9 H, s, 3 × SiCH 3 ), 0.91 (2 H, t, J 8.2, CH 2 Si), 1.21 (3 H, d, J 6.3, 8-H 3 ), 2.33 (1 H, ddt, J 1.4, 14.7, 8.1, 4-H), 2.37 (1 H, t, J 2.3, 3′-H), 2.41 (1 H, ddt, J 1.4, 14.8, 7.7, 4-H), 3.50 and 3.68 (each 1 H, dt, J 7.1, 9.6, OHCHCH 2 ), 3.91 (1 H, q, J 6.6, 3-H), 4.01 and 4.17 (each 1 H, dd, J 2.3, 15.7, 1′-H), 4.50 (1 H, dq, J 2.6, 6.6, 7-H), 4.57 and 4.64 (each 1 H, d, J 6.9, OHCHO), 5.24 (1 H, d, J 11.5, 1-H), 5.24 (1 H, d, J 15.9, 1-H), 5.36 (1 H, ddt, J 8.9, 10.7, 1.5, 6-H), 5.54 (1 H, dt, J 11.0, 7.3, 5-H) and 5.63 (1 H, ddd, J 8.0, 9.9, 17.7, 2-H); δ C (75 MHz, CDCl 3 ) −1. 5,18.0,21.2,33.3,55.2,64.8,67.0,73.9,79.5,79.9,91.8,118.5,127.1,133.4 and 137.0;m/z (CI) 328 (M + + 18, 95%), 281 (12), 163 (100) and 107 (71). Dodeca-2,4,6-triene 43.…”

“…The (E)-4-(2-trimethylsilylethoxy)methoxypent-2-enylstannane 16 was prepared by treatment of the allylic sulfone 14 12 with tributyltin hydride under free radical conditions followed by protection of the resulting hydroxypentenylstannane 15 using (2-trimethylsilylethoxy)methyl chloride, see Scheme 2. The 2-trimethylsilylethoxymethoxy (SEM) group was chosen with a view to its selective removal at the end of the synthesis; only the (E)-pent-2-enylstannane was isolated in this case.…”