A convenient route to α,β-unsaturated methyl ketones application to retinal analogue synthesis

Regeneration of bovine and octopus opsins in situ with natural and artificial retinals

“…The all-trans series of 5,6-ínms-dihydro-, 7,8-dihydro-, and 11,12-dihydroretinals were synthesized according to published procedures (Arnaboldi et al, 1979). The 11-cw-dihydroretinal series were obtained by condensation of the corresponding trans C15 aldehyde with the anion of (trimethylsilyl)acetone /eri-butylimine (Croteau & Termini, 1983), elongation of the 11-cis and trans C18 ketones with diethyl (cyanomethyl)phosphonate, and reduction of the nitrile group with dibal followed by HPLC purification. The 11ds-3,4-dehydroretinal was prepared from 3,4-dehydro-/3-ionone which was synthesized according to Surmatis and Tommen (1967).…”

Imine Azaenolates: Synthesis, Reactivity, and Outlook

“…With this approach, Croteau and Termini were able to synthesize substantial amounts of difficult to form Z-isomers of α,β-unsaturated methyl ketones (Scheme 13a). [95] The silyl imine was prepared using Corey's method (see Scheme 18a). [96] Using a TES α-silylated imine [97] Mills used lithium azaenolate aldol chemistry to form E-α,βunsaturated aldehydes, with complete E selectivity (Scheme 13b).…”

“…Depending on the reaction conditions, aldol‐type reactions of lithium azaenolates of α‐silylimines followed by elimination of the silyl group can be used to access either E or Z α,β‐unsaturated ketones and aldehydes (Scheme 13). With this approach, Croteau and Termini were able to synthesize substantial amounts of difficult to form Z ‐isomers of α,β‐unsaturated methyl ketones (Scheme 13a) [95] . The silyl imine was prepared using Corey's method (see Scheme 18a) [96] .…”

Carotenoids and polyterpenoids

“…~~ Compound (103) was then converted into the C,,, Wittig salt (104), which, on condensation with the C,,, 8'-apo-P-caroten-8'-al (1 0 9 , gave (2's)-plectaniaxanthin [(2'S)-3',4'-didehydro-l',2'dihydro-P,$-carotene-l',2'-diol] (106). ?O Another chiral endgroup synthon (107) was prepared from the chiral diol (108), which was in turn obtained by chiral reduction of the ketone (109) with baker's yeast or after resolution (by h.p.1.c.) of the diastereoisomeric esters of the diol with camphanic acid.…”

“…of the diastereoisomeric esters of the diol with camphanic acid. Compound (107) was used to prepare the lycopene and ycarotene derivatives (2S)-1,2-epoxy-l,2-dihydro-$,ll/-carotene (30) and (2'S)-1',2'-epoxy-1',2'-dihydro-~,$-carotene (31), identical to the natural products from tomatoes.38 The methylenecarotenoid aleuriaxanthin [ l', 16'-didehydro-1',2'-dihydro-P,$caroten-2'-01] ( 1 15) was synthesized, in an enantiomeric form, The sesqui-aionone (1 20) and sesqui-P-ionone (1 21), which are potentially useful end-groups for the synthesis of the CS0 analogues (122) and (1 23) of &,&-carotene and P,P-carotene, have been prepared by a route involving acid-catalysed cyclization of (124).73 Cyclization in the presence of H2S0, gave the bromo-ketone (1 25) and thence sesqui-P-ionone, whereas with H3PO4 the bromo-ether (1 26) was obtained, which could be converted into the sesqui-wionone.…”