Bulky protective groups

To control the stereochemistry of epoxidation at the 10,11-double bond in intermediates in prostaglandin synthesis, a bulky protective group was used for the C15-OH group. Epoxidation of the tribenzylsilyl ether yielded 88% a-oxide epoxidation of the tri-/ -xylylsilyl ether was less selective. ... 

Very bulky protecting groups at nitrogen (e.g., triphcnylmethyl, 9-phcnyl-9-fluorcnyl) afforded no effective stereoselection only a small shift to the mifi-product was observed 20-2 L... 

The triphenylmethyl function, also known as trytil (Trt), is a valuable bulky protecting group for peptide chemistry. Trytil groups confer acid-labile protection onto amines, but effective removal can also be achieved by catalytic hydrogenolysis. 

Locking donor conformation with bulky protecting groups... 

In order to built up the oxetane D ring, a bulky protecting group at C(7) which would survive the remainder of the synthesis and assure the P configuration of the substituents was necessary. Thus, 53b reacted with BOM chloride (EtN Pr2, CH2CI2, BU4NI, reflux, 32 h) to give 53c in 92% yield. 

Akiyama et al. (180) overcame this problem by employing ch/ro-inositol derivatives as chiral auxiliaries for the acrylic ester, which afforded dipolar cycloadducts with a high degree of stereoselectivity (Scheme 6.34). Formation of the major products [(55)-isoxazoline-5-esters] was suggested to arise from the s-cis conformer of acrylate 27, the minor product being derived from the s-trans conformer 28. The bulky protective group (in this case tert-butyldiphenylsilyl) would effectively shield the Re face of the olefinic double bond and destabilize the s-trans conformer 28. 

Inoue, M., Sato, T., and Hirama, M. (2006) Asymmetric total synthesis of (-)-merrilactone A Use of a bulky protecting group as long-range stereocontrolling element Angewandte Chemie, International Edition, 45, 4843 848. 

Through Differentiation of Primary Hydroxyls Using Bulky Protecting Groups... 

When a series of (Z)-4-hepten-l,6-diols, in which the secondary function at C-6 is protected by a bulky protecting group, is treated with mercury(II) acetate in dichloromethane (under thermodynamic control), the formation of 2-substituted tetrahydrofurans proceeds with good asymmetric induction120. 

We discuss the compounds presented in Scheme 1 and Table 1, where it is also summarized what kind of information is available about the different rings. For the successful synthesis of these compounds, the use of bulky protecting groups is mandatory. In Scheme 2, we have collected these various groups with the abbreviations used in the chapter. 

Scheme 2 Bulky protecting groups and their abbreviations used in this chapter.

Most of the three-membered rings discussed in this chapter are rather stable, their decomposition temperature usually being at 150-200 °C with simultaneous melting. This can partly be attributed to the presence of the bulky protecting groups, but it seems that the presence of more than one heavy element in the three-membered ring is also a stabilizing factor. 

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