Phosphoranes elongated

An example of chain elongation developed in palytoxin synthesis is given below. As shown in Scheme 11.53, compound 239 was reacted with the chiral phosphorane 240 to furnish the Z isomer... 

Approach to the preparation of elongated phosphoranes and their coupling reactions on a solid support (Scheme 134, Table 8, entry 24) [100] Under argon, a mixture of 2-bromo-5-acetylthiophene (644b) (1.14 g, 5 mmol) and TPPPS resin (phosphine resin) (643) (0.5 g, 0.8 mmol) in DME (Me0CH2CH20Me)... 

In another synthesis methylenephosphorane (137) was reacted with a-methoxyisobutyric acid chloride (138) to give the phosphorane 139 which was elongated to the alcohol 140 in a Wittig reaction with the aldehyde 141. Treatment with triphenylphosphine hydrobromide gave the Cis-phosphonium salt 142 and a Wittig reaction with the Cio-dialdehyde 20 provided 2,2 -diketospirilloxanthin (416) [16,17] (Scheme 32). 

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