Elimination Reactions. VIII. A trans Chugaev Elimination¹

Synthesis of Amaryllidaceae Constituents and Unnatural Derivatives

“…This synthesis was designed to produce the C-1 aldehyde that could eventually serve as as ource of unnatural derivatives (see Section 3.16). Thea mide nitrogen was then reprotected as its corresponding PMB ether,a nd the TBDMS ether was cleaved with TBAF.I nt he following step,C hugaev elimination [62] of an alcohol at C-2 provided olefin 63 in 22 %yield over three steps.C ompound 63 is ak nown intermediate in Padwas synthesis of 7-deoxypancratistatin [50] and its attainment formalized the synthesis of 7-deoxypancratistatin (Padwa prepared 2 in 7steps from 63). [60] Theo riginal aim of this particular strategy was the synthesis of aldehyde 61 and its conversion to 7-deoxypancratistatin (2)was of secondary importance.Itdid not proceed without problems,a se videnced by the number of quite arduous transformations required to convert 61 to 7-deoxypancratistatin (2)( Scheme 13).…”

“…In the final sequence of the synthesis,aldehyde 61 was subjected to Wilkinson decarbonylation [61] followed by reduction of the tosyl amide with sodium/naphthalene to obtain phenanthridone 62 (Scheme 13). Thea mide nitrogen was then reprotected as its corresponding PMB ether,a nd the TBDMS ether was cleaved with TBAF.I nt he following step,C hugaev elimination [62] of an alcohol at C-2 provided olefin 63 in 22 %yield over three steps.C ompound 63 is ak nown intermediate in Padwas synthesis of 7-deoxypancratistatin [50] and its attainment formalized the synthesis of 7-deoxypancratistatin (Padwa prepared 2 in 7steps from 63).…”

Preparation of reactions of nitrate esters of N-acyl serine and threonine derivatives

“…The above mechanism can only account for ciselimination products, even though there have been instances of varying amounts of trans-elimination products reported. 4 Briggs and Djerassi6 have recently found in their pyrolysis studies of epimeric cis-and írans-9-methylcyclohexyl-S-methyl xanthates and acetates that the cis isomers yield considerable transelimination product . Kinetic deuterium isotope studies led these authors to propose an ionic mechanism for the net trans-elimination process.…”

“…Treatment of A-acylserinemethylamide (1) and Aacylthreoninemethylamide (2) with fuming nitric acid and acetic anhydride in acetic acid gave exclusively the O-nitrate derivative (3,4) rather than the A-nitro derivatives. The use of fuming nitric acid and acetic anhydride alone gave lower yields of the nitrate ester.…”

The Sulfonyl Group and Its Effects in Organic Compounds

“…34 The activation of α-hydrogen atoms by the sulfonyl group is illustrated further by the reaction : 35 and the Tschugaeff pyrolysis of xanthates according to the following equation: 36 The inductive effect of the sulfonyl group, which is the cause of the more ready detachment of the proton, is also responsible for a reaction of bis-alkylsulfonylacetonitriles leading to very reactive imene derivatives. 34 The activation of α-hydrogen atoms by the sulfonyl group is illustrated further by the reaction : 35 and the Tschugaeff pyrolysis of xanthates according to the following equation: 36 The inductive effect of the sulfonyl group, which is the cause of the more ready detachment of the proton, is also responsible for a reaction of bis-alkylsulfonylacetonitriles leading to very reactive imene derivatives.…”