Thioselonocarboxylic Ester, Selenetane, and Dihydrodiselenine Complexes Prepared from Pentacarbonyl(selenobenzaldehyde)tungsten with π‐Donor‐Substituted Alkynes

Abstract

Pentacarbonyltungsten-coordinated selenobenzaldehyde, [(CO),W(Se=C(Ph)H)] (l), reacts with tBu-C=C-SMe(2)by insertion of the C=C into the Se=C bond to form in a highly regio-and stereoselective manner the a,P-unsaturated thioselonocarboxylic ester complex (Z )( . The formation of ( E ) -6 and (Z)-lOa is followed by isomerization until an (E)/(Z) equilibrium is reached. Complexes 3 and 7 were characterized by X-ray structural analyses.

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…156,163,166 In the reaction of 83 with carbodiimide, the supposed initial [2+2] cycloadduct 85 undergoes a cycloreversion to the isolated isocyanide complex 86, whereas the chromium analogue of 85 160 [188][189][190] with yneamines (eq 27) and other donor-substituted alkynes (OR, SR, SeR). [191][192][193][194][195][196][197][198] 208,209 resulting from a [2+2] cycloaddition/cycloreversion sequence in the reaction of 100 (M ) Cr, W; R ) Et, Ph, t-Bu) with ethyl diethoxyacrylate, undergoes an interesting cyclization reaction to give the pyranylidene complex 109 (eq 29), from which the corresponding 6-ethoxy-2H-pyrone, formally the result of a [2+2+1] cyclization reaction, could be quantitatively released by oxidation with DMSO at room temperature. The cyclization of 108 to 109 involves the formal transfer from the diethoxymethylene group of one carbonyl group (to the metal) and one proton (to C(3) of the pyranylidene ring).…”

“…In Scheme 50 the preparation and cycloaddition reaction of one example of either type is illustrated. 197 Via conrotatory ring opening, the 1,2-dihydro-1,2-diphosphete complex 365 appears to be in equilibrium with the 1,4-diphospha-1,3-diene structure (eq 97), 593 …”

“…Fischer et al have investigated the reactions of chromium and tungsten pentacarbonyl complexes of thio, seleno, and telluroaldehydes and ketones 96 [188][189][190] with yneamines (eq 27) and other donor-substituted alkynes (OR, SR, SeR). [191][192][193][194][195][196][197][198] The cycloaddition (∆H q values ca. 30 kJ/mol; ∆G q values around -150 J/(mol K) is regioselective (R 2…”

“…With tert-butoxyethyne as the alkyne, complex 98 (eq 96) is an unobservable intermediate which, as heterodiene, immediately undergoes a highly regioselective [4+2] addition with the SedC bond of a second molecule of 96 to give 364. 197 Via conrotatory ring opening, the 1,2-dihydro-1,2-diphosphete complex 365 appears to be in equilibrium with the 1,4-diphospha-1,3-diene structure (eq 97), 593 which can be trapped by the dienophiles maleic anhydride, N-phenylmaleimide, acrylonitrile, and benzaldehyde, giving the [4+2] adducts 366-369, respectively. The same sort of equilibrium, and the corresponding reactivity as 1-hetero-1,3-diene, has also been shown for the 1,2dihydrophosphete 370.…”

“…Reactions, as in eq 24 or 26, or the reaction of 35 to 36 in Scheme , where initially formed [2+2] cycloadducts consequently undergo a retroaddition by electrocyclic ring opening are not uncommon. Fischer et al have investigated the reactions of chromium and tungsten pentacarbonyl complexes of thio, seleno, and telluroaldehydes and ketones 96 − with yneamines (eq 27) and other donor-substituted alkynes (OR, SR, SeR). − The cycloaddition (Δ H ⧧ values ca. 30 kJ/mol; Δ G ⧧ values around −150 J/(mol K) is regioselective (R 2 = Me) and the ring opening is stereospecific (R 1 = H).…”