the invention relates to compounds of formula (1).(see form 1).where g is the group - and n (ch3) 2.n (c2h5) 2 or n - pyrrolidine, n is an integer equal to 1 or2; r1, r2 and r3 are independently of one another.a hydrogen atom or a methyl group, the reasons forcarbon may be otherwise identical or successiveon condition that at least one of the substituents r1.r2 and r3 may be different from, and y1 and y2 are each.the cooc2h5 cooch3 or group, such asuseful as intermediates in the synthesis ofretinoids and carotenoids.
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