Preparation of phosphorothioate oligomers

An azaphospholane of Formula VIb:

• ##STR95## wherein:
• Y is X or W wherein X is halogen, dialkylamino, imidazole, triazole or substituted phenoxy wherein said substituents are electron withdrawing, and W has the formula:
• ##STR96## wherein:
• Q is independently O or S;
• R.sup.1 is a hydroxyl protecting group;
• R.sup.2 is a chiral auxiliary of formula --C (R.sup.8)R.sup.3 --C(R.sup.16)R.sup.5 --CHR.sup.6 --NHR.sup.7 ;
• R.sup.3 is hydrogen, alkyl, cyanomethyl, monohalomethyl, dihalomethyl, trihalomethyl, --CH.sub.2 Si(R.sup.4).sub.3, or --CH.sub.2 --SO.sub.k R.sup.4 where k is 0, 1 or 2;
• R.sup.4 is independently alkyl, aryl, aralkyl or alkaryl having up to 15 carbon atoms;
• R.sup.5 is H, --CN, --Si(R.sup.4).sub.3, SO.sub.k R.sup.4 or halogen;
• or R.sup.8 and R.sup.16 are each H, and R.sup.3 and R.sup.5, together, form one of the structures ##STR97## wherein:
• R.sup.10 and R.sup.11 are H, alkyl having from 1 to about 10 carbons, --CH.sub.2 C(.dbd.O)OR.sup.22, --CH.sub.2 CN, --CH.sub.2 Si(CH.sub.3).sub.3, or o- or p-C.sub.6 H.sub.4 --R.sup.21 ;
• R.sup.21 is hydrogen, --O--C(.dbd.O)CH.sub.3, alkoxy having from 1 to about 10 carbons, --NO.sub.2, or --N(R.sup.22).sub.2 ;
• R.sup.22 is independently H or alkyl having from one to about 10 carbon atoms;
• p is 1 or 2;
• Z.sup.1 and Z.sup.2 are independently halogen, CN, --Si(CH.sub.3).sub.3, and --C(.dbd.O)OR.sup.22 ;
• R.sup.30 is hydrogen, --O--C(.dbd.O)CH.sub.3, alkoxy having from 1 to about 10 carbons, or --O--Si(R.sub.4).sub.3 ;
• R.sup.6 is H, alkyl or aralkyl having up to 15 carbon atoms;
• or R.sup.5 and R.sup.6, together with the atoms to which they are attached, form a 5 or 6 membered ring;
• R.sup.7 is alkyl or aralkyl having up to 15 carbon atoms;
• or R.sup.6 and R.sup.7, together, form one of the structures ##STR98## wherein X, T, and Z are independently CH or NH;
• or Z and R.sup.5, together with the atoms to which they are attached, form a phenyl ring;
• R.sup.8 is H or methyl;
• R.sup.9 is a hydxoxyl protecting group or a solid support;
• R.sup.16 is H, alkyl or aralkyl having up to 15 carbon atoms;
• B is a nucleobase;
• and
• n is an integer from 0 to 50.