Triflates conjugated synthesis

The key step in a short and efficient synthesis of pleraplysillin-1 (127) is the palladium-catalyzed cross-coupling of vinylstannane 125 with vinyl triflate 126 (see Scheme 33). This synthesis is noteworthy in two respects. First, vinyl triflate 126 is generated regio-specifically from the kinetic enolate arising from a conjugate reduction of enone 124 the conjugate reduction of an enone is, in fact, a... 

Methyl glyoxylate dithioacetal 292, after lithiation, reacted with a protected D-mannitol triflate in the presence of HMPA. This methodology has been applied to the synthesis of 3-deoxy-D-manno-2-octulosonic acid (KDO)462. A related ethyl glyoxylate dithioacetal 293 gave conjugate addition to different Michael acceptors, such as a,fi-unsaturated esters, lactones and lactams463,464. 

A range of polycyclic benzo b furans illustrated below was formed by the CuI/TMEDA mediated coupling reaction of conjugated aryl bromide-alkenyl triflates <07TL7578>, and a similar reaction was also found in the synthesis of 5-phenyl morphans <07H(71)881>. 

The key step in a short synthesis of ( )-tylophorine77 is an intramolecular double conjugate addition reaction. Reaction of the ( , )-unsaturatcd ester 1 (R2 = 8-phcnylmcnthyl) with ferf-butyldimethylsilyl triflate in the presence of excess of triethylamine in dichloromethane produces an 80 20 inseparable mixture of the indolizidines 2A and 2B78. Treatment of a mixture of 2A and 2B (R2 = 8-phenylmethyl) with sodium hydride in refluxing tetrahydro-furan for 2.5 hours gives the single indolizidine 2 A. Dioxanyl ester 1 furnishes, on reaction with... 

Salomon and his coworkers have over the years studied the influence of copper(I) triflate on the cyclization of non-conjugated dienes. In the present example the diene (170) is converted readily on irradiation in the presence of the catalyst and affords the alcohol (171). This is oxidised to the corresponding ketone. The intramolecular cyclization of the diene (172), using a copper triflate catalyst, affords the straight (2-1-2) adduct (173). This cyclization was used as an approach to the synthesis of RobustadiaJ B. However, it was shown that the proposed structure of the natural product was wrong and that the robustadials should have the camphahe moiety in their structure as shown in (174). ... 

The same two ketones featured again in a synthesis of ( )-lasubine II (910) by Pilli et al. (Scheme 119) (368,369). In this case, reaction of A -Boc-2-ethoxypiperidine (925) with enone 926 in the presence of trimethylsilyl triflate sparked off a remarkably efficient (90%) one-pot synthesis involving condensation (via an A -acyliminium ion to give the intermediate 927), deprotection, and intramolecular conjugate addition. The familiar products 921 and 922 were obtained as a 3 2 mixture. Base-induced epimerization of the mixture enriched the latter component, which was converted into ( )-910 by reduction with LS-Selectride (lithium trisiamylborohydride) according to the procedure developed by Comins (vide infra). 

The third possibility is an SN1 reaction with a vinyl cation as intermediate. This is unlikely when we are dealing with vinyl bromide itself 13 as the cation 14 would be very unstable. Notice that the vinyl cation would be a linear species with an empty p-orbital. Such cations are known when they are stabilised by conjugation 17 and the leaving group is excellent, such as triflate (OTf = CF3S020 in 16) but these SN1 reactions are rarely used in synthesis. 

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